Yes I agree- I think antibiotics do cause stomach problems sometimes. I haven't been able to take my MTX or Humira now as I have my 3rd chest infection in the last 4/5 months and on antibiotics. I'm just waiting for the results of a chest x ray to see when to start them again.
You mustn't just stop taking MTX without discussing it with your rheummy team. Do you have some anti nausea tablets? Your GP can prescribe them for you, might be worth giving them a ring?
YES I'VE CHANGED, PAIN DOES THAT TO PEOPLE.