Ok, so, I know you're feeling lonely. As social creatures, we all do. Being at year 12 myself and being single, I feel you fam. But I just want to say a couple of things.
First of all, it's okay to not have a boyfriend (I'm not trying to sound condescending, pardon me if you think so). I mean, I don't have a girlfriend while many of my friends (in my circle) are just engrossed in their relationship, albeit those lasts for about a couple of months at best, and then they move on to 'find' someone else. I find it rather hurtful, in a way. I mean, one minute they are here confessing their eternal love for each other and the next minute, they're the worst of enemies, generally speaking. I, from a 3rd person vernacular perspective, just look at them, and feel really sad (if that makes any sense? may it does, idk)
Coming to your situation, all I can genuinely say is that don't force it. Nothing good comes off from forcing anything. From what I've read from your post, imo, you're not doing anything wrong, infact, you seem like a chill person. Your time of finding that one person who loves you like no one else ever has/will, who'll live by your side supporting you till his last breath, who's genuine, who's pure in the heart, who helps others with unyielding sympathy, who loves the person that's inside of you more so than physical beauty; this person will come, have hope. I too have hope of finding/coming across such a girl/my (future) girl (hopefully!).
Maybe this said boyfriend/(and, if luck strikes and I hope it does, your future husband) will come tomorrow, or maybe in a couple of years once sixth form is finished, you (and even me for that matter) can't be certain. All we have to do is just be patient, wait/abide for our dream person. I know it isn't easy, being in this situation, but the dream of someday being under the laps of your significant other without any care for the world makes all this waiting worth it.
You said - "I'm sick of it tbh. I want a real relationship and I don't know what I'm doing wrong."
Well, I too am sick too, lol. You will get a relationship. not some half hearted one that lasts a couple of months, or years, but a genuine one. You're not doing anything wrong, just be you, plain and simple. No extra makeups, no extra effort, no extra/less of anything. If the person you find loves you for who you are rather than what you show yourself to be, that person is a keeper, for eternity.
There was this girl I used to like (since class 4) and still do infact. She once approached my in class 8 asking whether or not I like her. Me, being the shy person I am, said no, obviously. A couple of years passed and in Year 11, she began dating my bestfriend. To say I was devastated would be an understatement. But hey, I'm happy for her, if she's happy. But, sadly, that relationship lasted for about a couple of months. Now, they don't even see each other face to face, let alone talk. I'm still in fairly good terms with her although we talk waay less than in class 4. The point I'm trying to get across is that, I did a good job in saying no, in retrospect. Though she is a very talented individual, she has some problems that are visible and I found out that she isn't the person who I thought she was, but she has her own group and mostly hangs around with them now. Even after all that, I still love her. The human mind works in weird ways, ngl. And this came out like a rant, I just needed to get this out, idk, hope you saw the point I was trying to make
Lastly, I just want to say that I'm sorry that you got objectified by those disgusting/deplorable 'teenagers/male.' They are a disgrace to the society, objectifying women, I mean ef them. Anyways, this reply came out reaaally long, so I hope you found it useful in a way. And also, if this reply came out as too "advisey", know that my point wasn't to be all "preachy" and "wise". I just shared with you what I use to get out of this hole you're currently in, once in a while. So, yeah, keep faith in fate and just keep on being genuine and most importantly, be patient. You're boyfriend/SO will find you and you, will find him.
A fellow Year 12'er that's in the same boat,
E.