IBS & Indigestion/Heartburn possibly?

My husband has been diagnosed as suffering from IBS a few years back. Since those days he knows basically what he can eat and what his body will not tolerate.
For the past 2 weeks, he has developed a indigestion/heartburn type symtoms - bloated feeling, pain just below the ribcage moving to the centre and constant burping.
Although he is overweight, he goes running, plays squash and goes to the gym quite a bit.
Recently, he has also been quite stress with a lot stress triggers and anything at the moment can trigger that emotion with him.
I was wondering if he is indeed suffering from indigestion or what it is. He has an appointment with the GP on Friday and currently he takes Zantac to help ease the pain.
Initially, on the first night that he had this problem, he had acute stomach pains. Now the pain is achy but not prolonged and not acute, it comes and goes. He has had the chills, though, for the past 2days. Our GP, needless to say, isn't the brightest tool in the tool shed and has made umpteen mistakes before, so, confidence in them isn't really there.