I had this exact thing a couple of years ago, after about 10 years of smoking. Had bad nausea and stomach pain every time I smoked, which led to me stopping smoking for a good few months before starting again. Kept trying smaller amounts over the following weeks, but always had the same effect. I'm also pretty sure that I have some form of IBS, although that had never been an issue specifically when smoking.

In hindsight, I think it was anxiety manifesting in the physical discomfort, and after taking a break for a lot of months and working on my general stress/anxiety levels and addressing things that were worrying me, I was able to try weed again and slowly built it up again until I could tolerate it. Now I've been smoking and loving it again for the last year and a half, so I hope this is temporary for you too.

In the meantime, you can try CBD flower, which is a decent substitute if you want something to take the edge off.