Lost my ability to drink, need help.

I used to be able to drink like no tomorrow but now only a shot can push me over the edge.

Recently ( about a month ago) I went to a party and got super drunk off of crown royal. I spent the next morning throwing up for about 3 hours feeing like shit, and I had never had a hangover before, until this. Tonight I only had two shots of Bacardi mixed with sprite and it took me an hour to finish drink because I felt like I was going to puke after every sip.

Unfortunately I feel like I may of developed a alcohol intolerance and lost my ability to get drunk forever. The only time I ever drink is at parties. I'm hoping if anyone has had the same problem I have and has overcome it, please tell me how you did it.