I'm not a body builder, but I workout regularly, I have had the exact same symptoms as you. I can't confirm that these symptoms arose due to a night of binge drinking, although I have had a few of those. I have the gas (although it is not always foul smelling) and the distended lower abdomen. I have also noticed what appears to be undigested foodstuffs in my stool, particularly grapefruit which I eat everyday. I also take a protein supplement which mixes with water.
I told my doctor of my symptoms and he said that it was probably hemmoroids, which it wasn't, for the simple fact that I have never had them. I didn't hurt to have a bm, it felt like I was pushing my stool through a penne pasta maker. The symptoms persisted and my doctor said that sometimes there is an involuntary tightening of the inner anal sphincter, which would restrict the size of the stool.
This seemed feasible except I have had movements of what would be a relatively regular shaped and sized 'log', however it consists of a continuous pencil thin stool folded in upon itself, which would suggest to me that the restriction occurs before the anal sphincters. The diameter of the my stool, when solid, varies from pencil thin to about an inch, and is never completed round.
I had an analoscopy, (not as deep as a colonoscopy) and it revealed nothing. I also experience constant fatigue. As for the undigested foodstuffs, for about a year I took digestive enzymes and that seemed to lessen the occurence, although I have since stopped because I am afraid that they may be masking an underlying problem. The bloating and stool restriction never stopped during the time I was on digestive enzymes, although I did seem to have a bit more energy while taking them.
If you have learned anything from your doctor visits, please let me know.