Small boy carrying the egg of a very large dragon. By the end of the pregnancy, the boys' tummy is so big it dwarfs him and prevents him from getting around unassisted. His dragon mate has to help support the weight of his stomach to get him from room to room.
When labor begins, the size discrepancy between the boy and the massive egg is so large that it takes several weeks. Contractions last for over half an hour and hardly make any progress. The dragon tries to keep him walking around as much as possible to help the egg progress downwards, constantly forcing the heavy weight of the egg against his tight little cervix, which takes far too long to open wide enough to let the egg squeeze into his birth canal.
The birth is even worse, the small boys narrow hips barely holding together with the solid mass of the egg trying to break him apart from the inside out. He crowns for over a week around a big heavy egg that's easily the size of a bowling ball, if not bigger. The dragon holds his body together with magic, which is the only reason he doesn't rip apart trying to deliver the impossibly big egg. He births in all different types of positions to try and get the egg out, on his hands and knees, on his side, standing (with the assistance of his dragon mate), even walking all the way to the hot springs with the egg spreading his hole wide open in hopes that the hot water would ease the process. The egg splits him so wide open he can't even shut his legs anymore, and he begins to wonder if he'll be stuck with his pussy wrapped tight around the egg for forever.
When he finally gives birth to the dragons egg, it's been over a month since he pushed for the first time, and his cunt is entirely wrecked from being stretched so wide for so long. Luckily, the dragon uses its magic to make sure he's healed up nice and extra tight for the next egg.