Since Mid October I've Had A Sour Stomach With Diahhrea

Since mid October I've had a sour stomach with diahhrea (usually resulting in diarrhea once a week or sometimes I'll have two weeks in between episodes). After the first bad couple of diahhrea bouts in October, I saw blood and sometimes bloody mucus in my stool. This persisted even with solid stools so I made an appt with a gastroenterologist in November. Gastro doc said blood was likely due to hemmroids (I even showed her a pic of my bloody stool to show her the color of the blood). She did an abdominal sonogram and bloodwork, which all came back normal (spleen was on the large side of normal but that's it). I brought in a stool sample the next time I had diarrhea in late November and that too came back "negative."

Doc says that next steps would be to do endoscopy and mini colonoscopy to look inward for the problem but the office nurse suggested that maybe it was just stress.

I didn't like the bedside manner of the first Gastro doc (she didn't want to talk at length with me - just dismissed me with the suggestion for a endoscopy / colonoscopy) so I'm now waiting for a 2nd opinion with another doc. I'm not opposed to having those procedures but I'd rather do it when a doc I feel comfortable with.

In the meantime, I started taking Metamucil to try and regulate my stomach and the blood stopped for a week or two...until tonight, when I saw bloody mucus again. I've also been having a slight pain / tenderness in my upper left side under my rib (on the side and towards my back). I'm trying to eliminate dairy to see if that helps but this is day 1 of that and I still felt a sour stomach most of the day.

So, I guess my question is, if my sonogram was clear, what could this illness be? Does an abdominal sono look at my colon? Does this sound like ulcerative colitis? I don't have terrible pains but I do sometimes have slight pain and discomfort (but not constant or debilitating). I've also been very bloated. On another note, I've been burping constantly for the past few years (it started during my first pregnancy 5 years ago and never really went away). Sometimes it feels like I have air trapped in my body that I can't fully get out - the burping attacks can be intense. BUT, it never really happens when I'm talking to people and mostly occurs when I'm driving or sitting alone. Would that suggest that it's psychosomatic? Is this related to my sour stomach / diarrhea / bloody stool? Any help you could give would be appreciated!