Hey, I just read your post and can totally relate to everything that you have said here. Im also at Sheffield Uni, in my second year, and from what you have said I have also had similar experiences. Likewise, in freshers week and towards the beginning of my first year, I met lots of people and went out lots, but didn't really feel that close to any of the people that I met. I was actually quite homesick and felt very lonely. I think I really missed having really close friends around. The way that my course was structured didn't really help either; I do history, and there is very little contact time, so again, it was difficult making good friendships.
However, I found that after Christmas, the people I lived with (in halls), started to calm down a bit and people began to show their true personalities. This was when I started to form my close friendships. I know that its a bit different living in a flat, as there are fewer people, but those flatmates that you don't really get along with may yet suprise you. Another thing to remember is that there are a lot of people who are feeling this way, but they are doing a good job of hiding it. One of the bubbliest, loudest people on my corrider last year turned out to be the most homesick and miserable of the lot of us, yet it took a long time for us to realise because she kept it so well hidden.
Aside from hoping that people will change, there are other ways that you could maybe meet more people, or get to know your current friends a little better. I agree that a lot of societies do seem to revolve around drinking, but not all of them do, so maybe check the union website, which has a list and see if there are any that you might fancy joining. Maybe also see if your department has a society, as this can be a good way of meeting more people on your course. I don't know if you have thought about getting a part-time job, but this is another good way to meet people, especially if you work in the union.
I think the best thing to do right now is not to panic too much about this, as from what people have told me it seems to be fairly normal, and maybe concentrate on developing the friendships you have already made.