Why does Captain Morgan and Diet Coke make me feel sick to my stomache Read below

Alright, I used to drink Captain Morgan and Diet Coke all the time. I used to drink a lot of it. After a while, I started not feeling so well. I would start getting sick to my stomach. I stopped drinking it for a couple weeks, then started up again with just the Captain Morgan. I drank it straight with no soda. I would also have a few shots of tequila afterwards and get buzzed and drunk.

I decided to have some soda with it again last night, and I felt ill. Why does mixing the Captain with the Soda make me ill, but the liquor straight makes me feel good?? I just don't get it.

Every time I go out the only thing i drink is Captain morgan and diet coke...for years now and i'm gonna be 25 so probably started when I was like sixteen but ne ways thats all i ever drink and I LOVE IT...but I've read in a million magazines that it is not good to drink diet soda and liquor only for the simple fact that because it is diet soda something in it makes it so that you get wayy drunker wayy faster and that is probably why you are getting sick. I think I'm just immune to it becasue it's the only thing i drink and i don't do shots or anything. Hope this helps!!!