A biggish belly, huh? Well, normally pregant mice don't start showing until about 14 days, and some don't even at that point! But I suppose there are always exceptions, and it is definitely possible that this early showing is due to a large litter! Also, have you been feeding her extra fat and protien (like puppy bisquits, etc.) to help her prepare for nursing, etc? Cuz that could contribute to weight gain! hehe
As far as blackjack goes, haha, maybe he just mated the first time and now he's in "mate mode", thinking that there might be a chance he can mate again. I bet he'll get over it. But that is funny! Maybe you should buy him a pink tutu! LOL, just jk.