GH gut...without the GH

I guess the title of the thread could also be summarized as a "distended abdomen", but i thought the GH gut thing would garner more looks/responses. Anyway, here's the problem: I've gone from a smooth but lean 205 or so this summer to 250 lbs as of yesterday (the 205 was artificially low as a result of poor dieting, so much of the gain was getting back to ground zero, but a good chunk of it is hard-earned new muscle as well). Additionally, i've managed to keep a decent amount of definition, though as soon as i topped the low to mid 240's it began to dissapear at an accelerated rate. The BIG, rather HUGE, problem is that during this time, I've developed a pretty sizable gut. The gut, however, has little in the way of fat (i can hardly pinch very much and the abs are still "slightly" visible...at least for a few more days) and is rock solid, it just sticks out there much like the GH guts of some pros....making my chest look significantly smaller in the process.

I have a few theories as to why this might be the case, one being that the amount of food i'm taking in, well over 5,000 calories a day currently, has produced an expanding of sorts to my stomach (may be my imagination, but it seems more pronounced after eating). Another theory is that my current workout routine, a traditional powerlifting routine, may have caused this, not because powerlifting routines themselves cause it, but because my inexperience may be leading me to breath and hold my breath incorrectly in the power movements, possible building the abdominal wall outward. Lastly, i've been taking creatine for the first time ever with any regularity and duration...could that do it (a long shot, but still)? Oh, and i'm still natural (hopefully not for much longer) so it's not a result of any gear.

Even if you don't know waht's caused it, how does one get rid of it most effectively. Obviously my PL'ing routine focuses heavily on ab strength, as all PL'ing routines do as I've seen...so i've been diligently focusing on pulling my bellybutton in towards the spine in an effort to mitigate this problem. Additionally, i've been doing about ten minutes worth of vacum poses before bed at night. Anyone else remedy such a problem? If so, how? Thanks.