When I smoke marijuana for medicinal purposes I sometimes cough so much that I throw up. I feel like I have smoke in my stomach.

Take smaller hits, duh. I shouldn't have to explain that. You may not even need to inhale,just exhale it through your nose.

Don't swallow the smoke. Don't use a bong, it pushes the smoke into your stomach. Smoke the smallest amount needed to get the effect.

I used to be a heavy pot smoker. nowadays, I think it's pointless.  But anyway, I used to do huge bong rips all the time, and it was not uncommon to belch up little puffs of smoke afterward.

But, you know, pointless. 

Puff a little now and then, or every once in a while. But whatever you do, get on with your life.