Alright, so I went and saw one of the MSU Sports Medicine doctors last week and he said it's one of two things (and not a groin pull like I originally thought). Based on physical tests he had me do, it's either a stress fracture of my lower pelvis or a sports hernia. The first one wouldn't require surgery but absolute rest while the second one may require surgery. Going for the MRI on Thursday to confirm what it is for sure.
So all winter I've snowboarded on this thing thinking it was a pulled muscle and that I probably wouldn't make it worse when in fact I was putting myself in danger of making it much worse. It also explains why small falls onto my tailbone hurt so much more than usual. Moral of the story? Don't wait to get shit checked out. Hopefully I can right this thing before next season.