My ex-girlfriend of 5 years once told me "Sometimes people spend birthdays alone" as her reasoning for not seeing me on my birthday, two years in a row. Simply because she didn't want to. There are some legit nasty pieces of work out there. It's all about stepping back and looking at the situation..

People don't come to you, sometimes you have to do the legwork. Birthdays are one of those things that slowly get forgotten along the line and it's one of things where, even though it's your birthday, people can sometimes be too busy with their own lives to remember. Everybody forgets birthdays, even though we all want to feel special/appreciated/noticed. It's weird, and even though it's your own birthday, sometimes you have to be the adult and plan something for yourself, reach out to people and plan something and set a date/place if you want something to go down. (Depending on if you have anxiety issues, this could be a challenge, but it could also be good practice for the next part.. )

Put yourself out there. So much easier said than done. It's hard, really hard. But amongst things you can practice, human interaction is one that pays off really well, and just like anything else, you can get rusty. As someone with severe social anxiety it's honestly one of, if not the hardest thing about life. Putting yourself out there and trying to make connections with people. You said it yourself, you've only just started a new school - and you're acting like all is lost. This is your chance to get yourself comfortable with your peers, and meet new people. You need a balance at school, so concentrate on the study - don't concentrate on the social side of being at school because you're going to have a bad time. Don't be scared to work with or approach people in class, it's a great way to make friends. Don't force it. Be patient and good things will come.

Back to my original point. My ex, was an asshat. There are horrible people out there, but there are also a lot of good people too. Don't be afraid to give people a chance and immerse yourself. Because in situations like these, you're not alone! And sincerely hope this advice helps :)