It sounds quite similar to some of the problems I had when I had gallbladder problems, lots of ridiculous burping and air in my system and had to avoid large meals and fatty food as much as possible. I used to cut food up really small too to help with digesting it where possible.
I started reading food labels like a hawk and went on trying not to exceed 3% fat in anything, lower of fat free if possible - it's a bit of a shock when you start reading them and realise how much fat is in everything, especially ready meals, even some of the "healthier" ones!
I'd get to you doctors soon. I had my ultrasound scan and a few days later my GP rang me to say I had gallstones and a distended gallbladder and to look out for pale loose motions and dark wee. I pointed out I had them already! Two days later I felt really really ill and ended up seeing the out of hours doctors at the hospital and being send to be admitted via A&E as my gallbladder had got infected (acute cholecystitis).
Really wish they have taken it out then as even with the infection settled, it made me really ill until I had it taken out 4 months later, by which point it was going septic and had split.
I hope you get it sorted out soon. If it is that, there are quite a few people on here who had had gallbladder problems if you repost.