Similar to a stomachache, one gets a poopache when they have not flushed their body of waste for an alarming number of days. In other words, the ache a person might get when they have to poop but hold it off. May or may not be accompanied excessiver with gas, stomach pains & aches.
Boy: I haven't gotten a chance to take a dump in the longest time and my stomach hurts like hell.
Girl: Damn, sucks for you. You must have a poopache.
Man: My stomach fucking aches, I'm passing gas, and I get these excruciating pains in my abdomen, what the hell is this shit, Doc?
Doctor: Looks like you have a poopache. No worries, just take a dump ASAP.