Coffee?

From time to time, I think I'll try drinking coffee to find out whether the reaction to it that I developed after radiotherapy has subsided. Today was one of those days. The result was the same: nausea, headache, abdominal cramp. Must remember not to drink coffee... The health professionals I see tell me that there's no reason for this, given nothing else makes me react like this, but the fact is that it didn't happen before I had radiotherapy. Coincidence? I doubt it!