I'm also 18 and started uni not long ago too, I can definitely relate to this. In a way, I'd say that it was slightly worse for me because I didn't get into Uni accommodation, leaving me to find my own private accommodation. i'm currently with a bunch of random people, all older than me, most are older professionals who are already well-established. As a result, I've had to depend solely on my course mates and societies to make friends.
As with you, i don't have many friends here either. There are people who I can work with and talk too on my course, but they are all commuters and tend to go straight back home after lectures anyway. I see other people's university experiences, little things like you said about others' taking Halloween pictures together and I feel as though I'm missing out on something big.
In the end, you and I have only been at university for what... a month and a half? I met some of my closest friends in secondary school only after 2-3 YEARS. The people who i were friends with in year 7, for the most part, didn't remain my friends throughout my secondary school years. The same can be applied to university; just because you haven't clicked with anyone in the first month or so, hardly means that you never will. I get why that seems difficult to believe; after all, though it's only been a month, I can already see people forming distinct clicks. But as it was in secondary school, there is no guarantee that these groupings will last forever. There are inevitably some people who are in exactly the same position as you right now, in fact, and it would do you good to perhaps keep an eye out for them.
Don't be fooled by the appearance of other universities; my university looked absolutely spectacular before I actually started attending. Ultimately, it's the people who you meet who make the experience, not the facilities. You could be in an absolutely trashy, tiny library and still have a whopping time if you are with the right people.
These past few days, I have been feeling a little down. I often imagine having someone who I could go out with at 2am, just walk through the city or something, take some pictures. But then I remember that very few people are actually living like this at university. In a way, I feel that you might be looking at this in too much detail. I've taken offhanded group selfies with a few friends from my course, I sit with some of them to study in the library when we have nothing else to do; but this doesn't mean that I'm super close/comfortable with them and after these brief meetings, we simply part ways.
So don't be misled by all of these amazing pictures that you see others' posting. i know people who met up with complete randomers at the club during freshers, posted photos of them having a great time, but never even saw each other again afterward.
I would suggest just talking to as many people as you can. There is a girl in my lectures who always sits by herself. The other day, I asked if she was saving the seat next to her for someone, she said no and I ended up sitting next to her. She was incredibly shy, didn't really seem to know what to say, but as someone who used to have crippling social anxiety, i just kept trying to chat with her. I hope she's somewhat opening up to me now. You should try something similar. One of my biggest problems (maybe one of yours too?) was that I constantly expected people to either come my way, or for things to fall into place.
That doesn't happen.
You need to be proactive, stop wallowing in your room and feeling sorry for yourself, and talk to as many people as you can.
I understand that you've tried several societies, which is great. Societies for me have sort of been a saving grace. Sports societies like the ones that you have joined are usually very good for meeting people, so I would just join as many as you can. Even if you don't particularly enjoy the sport itself, just being out of your room and surrounding yourself with other people will 100% make you feel a little less depressed. If you end up standing next to someone, just start basic conversation. Ask what their name is, what course their doing. It seems like such a stiff way to make friends, but everyone does it at the beginning, and it works very well.
Do you have something like a film or a gaming society? I personally find that these societies are a lot easier to make friends in. I went to yoga society not long ago and there were just big-booty health-nuts lol, which is why I find sports societies can be a little stifling. In film society, we sort of just sit together and watch films. Because you're sat in one place for a while, you also get to know the people around you pretty well.
You said that you enjoy being around "clever" people lol - not sure what this implies and I hope that you're not actively repelled by non-geniuses (jk) but is there something like a chess club? Everyone is going to be wanting to show of their intellectual abilities, it might be quite stimulating for you.
The worst thing that you can do is hole up in your accommodation and feel bored and miserable. Even if it's not directly making friends at university, try and be active. I find that people who are more active (actually, I believe it's scientifically proven) are more confident, and thus make friends more easily. Even though I am a complete couch potato, I signed up for the gym. The gym near me is very student-oriented, so I'm hoping to meet others' there too.
Don't forget that your university is in London. I think that it's about the same distance from central as my Uni is. Be spontaneous; hop on the train at 9pm and go to Starbucks at Leicester Square. Appreciate your own company before anyone else's.