Have you talked to the GI yet? If not, I would suggest to call and let him/her know.
I had nausea and horrible diarrhea only after taking 2 days of 6MP, and I was hospitalized for fluids a few days later and told to stop 6MP immediately even though all my labs came back okay.
The dose and/or the new med could be the problem, but I definitely talk to the GI.