I have had similar problems facing turning 21 and not knowing how i'm going to handle the alcohol I want to consume... My best advice if you have an underlying mental health issue, is to just hang out & drink slow & maybe serve as a DD for the night. I only have 1 or 2 max when I drink due to the weird feelings I get. It sucks but if you drink this way people will understand your situation and there shouldn't be any problems. I have tried hanging out in bars trying to keep up with the crowd on drinks and it's just not possible. The times I've done this I end up getting embarrassed feelings and get afraid that im going to have to talk to someone I know... LOL

Hope this helps and GL!