my son hit his head hard!

Oly • SAHM who loves movies, nerdy games, music and cooking
Husband was watching him play in the tub and he slipped and hit his head trying to stand, the corner or the tub, 5 minutes later it's already purple and goosed up! Is he okay? We just spent over 6000 on a goose egg in February just for them to tell us he's fine (we figured but the pediatrician made us go in) so I'm a little hesitant but also worried. What should I be looking for?