Reality is it might not get better for you. The biggest personal regret in my life still some 6 years later is choosing a new sixth form because it was deemed to be more prestigious for medicine, but I never considered the fact that I was leaving all my good friends behind in the old one and that the new one could be full of a load of *******s, which it was. All in all it made for a pretty depressing 2 years, the first wasn't so bad but coupled with uni stresses in the second year, and the general angst of being a teenager still finding themselves it made life pretty tough.*
It does get better afterwards at uni if you go there as the people are far more open in general, but that's no consolation for you. Though in some of my classes I had one or two people I got along with fine, I didn't make any perma friends I hung around with outside of class (partly due to not sharing more than one class with anyone), and in one subject I was pretty much excluded from any groups, surrounded by idiots and all in all had a miserable time of it. It went on like that for a year, and I've seen others in that situation too and it's not a good one as the longer it goes on the harder it's too resolve.*
This probably isn't great advice, but mine would be as follows - 1) Try and find other people who aren't in a group, and tentatively work with them on group projects. Or just sit next to them in class if there's space. I wish I had done that in the lesson where I was by myself, as there were a few spaces next to others elsewhere. Though obviously this one's tough as it requires you to be proactive, and it's always a nervy thing to go upto randomers unless you're confident with that sort of thing.*
2) I'd recommend this more than anything - it's what I really wish teachers would take more note of and really the few cases I've noticed teachers taking active note of it really highlights the difference between good and bad teachers. Shoot your teacher/s an email in whichever class you're struggling with people in, and just explain that you have no one to work with in group projects / general work, and would he kindly advise on what to do or potentially chose partners for some of the group projects so that you get to meet / work with new people. If they're anything worth their salt they should be more than happy to help, and a supportive teacher on your side can make the world of difference.
Let me know if that helps or not, I'd definitely recommend considering shooting an email to the teacher, I'd be happy to write you a reasonable email to send if you wish too (though don't get on here often sadly so might not reply right away).*