Oh my gosh I just started getting the same issue...every time I eat something, about 5-10 minutes later, I get lower abdominal gas...the kind you get sometimes before diarrhea. But then it just goes away after about 5-10 minutes. Plus I think I'm intolerant to the whey protein in supplements so I just ordered an egg protein based supplement because I'm definitely not getting enough protein.
Oh and I'm on the same post-op diet as you. They had me on full liquids for 7 days after I went home, then on pureed for 7 days and now I'm in the soft food stage and it should be much easier but this stage is where all the intestinal distress has come into play so I'm going to try and switch up what I'm eating...lean away from the yogurt and cottage cheese and canned chicken and try some flaky fish, more soups and some soft cheese.