Like you I suffer from depression, even though I have good health, a good marriage, a nice house that is paid for, an excellent pension, and lots of money in the bank.
But that does not stop me being depressed so don't apologise for it.
Things like this can often be caused by a chemical imbalance in the brain and drugs can put that imbalance back to "normal" so I would go and see the doctor.
After all there is no point in suffering if you don't have to.
I wont say "snap out of it" because I know it is hard to snap out of it.
But you say you will feel bad next to your friends so you need to concentrate on what is making you feel bad and try to work on it (are you overweight perhaps?).
A few years ago I knew a lady who modelled outsize clothes, she was a large lady, but made the most of it with nice clothes and hair and make up.
So make the most of what you got, treat yourself to a new outfit, and wow all your friends when you go the next event or to the wedding.
Good luck.