I'm 24 yrs old man whenever I do toilet I feel like vomitting can anyone tell me why?

I'm guessing that by do toilet you mean doing a number 2. If so, then might I ask, have you been out of the country recently? You may also need to provide more info like what the stool is like and if you do actually vomit, how long has this been going on and have you spoken to your dr about this?