hmm well have you tried to gently palpate her recently? If her latter half feels really soft, like waterballoon-ish then she is definitely gravid. Even holding her and letting her body hang freely for a second should let you see whats going on.
Either she is just laying funny and has a huge case of sausage butt or she is gravid;but being gravid and not having shed in 3 months doesn't sound very accurate?