Why Does My Stomach Hurt Whenever I Smoke And Have Nausea, Tightness And Loss Of Apetite ?

Hi there, I've been trying to quit smoking pot and tobacco, I mix them into what people call a "popper", I generally use more tobacco then weed. I have cut back substantially the past week, and now am down to two at night before bed. I used to notice I would have stomach issues when smoking consistently, but they weren't that bad, they were bearable, just lost appetite some days, and a little nausea, but now that i'm cutting back, when ever I smoke the little I smoke, it absolutely hurts my stomach, either the night of, or the morning after, nausea, tightness, diarrhea, no appetite for hours into the day, I guess my question is weather or not it's the tobacco or the weed, just for future knowledge, so that I may cut the tobacco out first, then the weed, so I'm not feeling these symptoms in the weening it out phase, or if it's best to just go cold turkey at this point.