Hi,
I can understand what you are feeling,i feel like you at times. First thing i can suggest is try to think about what you really enjoy, hobbies etc and join a club for that hobby if you can, see if there are any evening classes you might like to do (and might help you get a different job), do some volunteer work, take up a sport or go to the gym, just anything so there is more to you life and somewhere you can meet people but there isnt too much pressure on you to be socialiable and there is something in common which you can talk about.
Some of the feelings you are describing fit in with what you can call social anxiety. Search for this on the net and there are alot of websites which can tell you more about it. I believe i have mild social anxiety so if you want to pm about this thats ok. I've had councellling through uni which has helped to some extent, cognitive behavioural therapy often helps. It might be something you could consider. This book - Overcoming social anxiety and shyness by Gillian Butler, is really really useful.
Christmas sucks, end of, its probably going to be difficult but hang in there. There are lots of people feeling the same as you- sending you a hug!
When people go away to university it is very difficult to stay in touch with people from home, it might be worth ringing or texting your friends now that they've come home for the holidays.
Do you know what kind of job you'd enjoy? Maybe thinking about this and getting some work experience could help as it means theres something to plan for and think about.
Another thing i'd advise but i might not be what you like to do is to save up and go travelling. You could just go for a little while or for a long time, far away or near, do work in a different country or just travel around, but its something to aim for, have new experiences which you can tell people about and it might help you to think about your future!
Just maybe trying to raise your confidence and self esteem might help it'll enable you to try new things and talk to new people and slowly you'll get new friends.
Anyway, i don't know if this will help or not but this is just some of my thoughts, sorry if it doesnt really make any sense!
Sarah xxx