Yellow stool/mild abdominal pain with Uc

I've had Uc for 19 years and have went thru whole gamut of meds.  I am currently on Colazal and 6mp - I am unable to take mesalamines due to intolerance.  Last December I was hospitalized for 3 days for severe abdominal pain and a full body rash.  I have had Left sided all these years but when I was hospitalized, my whole colon was inflammed shown via CT Scan.  Before my hospitalization, I was having yellow stool only - no other symptoms of Uc.  So I called my doc and he just wanted a stool sample.  I never had a chance to get it to him because I went downhill pretty quickly.  After I got out of the hospital, things were a bit shaky for a while but I am feeling better again. I had my follow up with my GI and he didn't seemed too concerned about the yellow stool; I was able to give him a stool sample and nothing was found.  Now I am experiencing the yellow stool again with mild abdominal pain.  Not as bad as before thank goodness!  I also have been burping a lot and having stomach and intestinal pain after I eat.  I already take Prilosec for acid reflux btw - not sure if this has anything to do with what I am experiencing.

Do any of you happen to know what would cause this cycle of yellow stool and abdominal pain?  I've had the yellow stool off and on over the years, but it was more in the diarrhea form because I was flaring; I also had some green liquid mixed in.  It comes and goes.  I have an appt in a few weeks with my GI and I plan on bringing it up with him again but I just wanted to get some input before I go see him.