The problem is getting into a cycle, of negative behaviour and expecting negative reponses.
The good news is you are sooo young and have plenty of time to work on this.
A really good way to make friends and make it easy for yourself...is by doing a hobby, do you like sport? Tennis, hockey, rugby....or reading...perhaps join a book club.
As a first step, it would help if you could put yourself where other people will share the same interests as you, so immediately you have something in common.
After all, those of us with DC, that is all we have in common when we go to toddler groups alone or join NCT groups, nearly all sentence openers are..."how sweet, how old is she/he whats their name" Even for confident people, its hard!
Although it should not count one bit, appearance does count.
Do you present yourself well?
Apart from feeling friendless, are you comfortable with your own company, are you confident?
This comes across in body language, slouching, trying to make yourself seem small, the way you stand....a tiny bit of confidence helps enourmoulsy...
Always remember nearly everyone new you speak too, also feels nervous...and everyone's number ONE FAVOURITE SUBJECT IS THEMSELVES.
Work on posture, presentation, eye contact, compliment someone, ask them a question seem interested. It may only be a moment of conversation but the next time you see them, you can nod or aknowledge them.