Hello Jasmine R
Welcome to the forum. I am sorry to learn you feel so sad and lonely at this time. Are you still in foster care or do you have a place of your own?
Friends are really great but family does make us feel happier. May I ask why you do not have contact with your birth family. I see you think they treated you badly but not sure why unless you mean that it was because they put you in foster. No need to answer this question if it is too upsetting.
As you cannot have a family birthday party can you arrange a party of some sort with your friends. I know the COVID19 restrictions will have an impact on getting together with friends especially if you live in Victoria. However you may be able to go out for a meal somewhere if restrictions have been lifted in your area.
I gather you do not have any professional mental health help. Have you talked to your GP about this? I have found GPs good to talk to about these things. They can also refer you to someone else if necessary. Feeling sad for every birthday is not good. You would manage better if you had some way of coping with these feelings.
Please continue to write in here.