What the deuce... -_- (back pains / exercising)

So 10 years ago, I busted my tail on some ice and "shifted my pelvis" out of alignment. Saw a chiropractor off and on, but honestly it felt better when I didn't see him, so I quit. Haven't had any issues for a few years, except for if I move wrong, and that only lasts about a day then it's back to no pain. Took the trash out the other day and tossed it from the porch into the can (maybe 7 feet) because it was semi-light, came in and leaned over to put the new bag in - boom. excruciating and radiating pain. It's not in my lower back, where it usually hurts. This is like... tailbone / hip bones / lower pelvis region. I thought maybe sciatica, but *shrug* I'm just an EMT, wtf do I know.

Here's the wonky part: it hurts more to sit than it does to stand, walk or lay down. Walked the zoo the other day for 3 hours, best I've felt all week. Last two nights, an hour on the treadmill around 2.5 - 3.0 bc I didn't want to jog and jar my pelvis. No pain at all the whole workout and for at least an hour or two afterward. If I lay down on my stomach in bed, no pain.

But Jesus God let me try to sit at work or flipping drive somewhere and its the most unholy pain I've ever felt. Its at it's worst about 10 minutes after getting up after sleeping all night until I can manage to pop whatever pain killer I can find. Then it dulls down to manageable while I work until I can get on the treadmill for sweet relief.

Any ideas? I've never heard of exercising making something better *shrug* maybe it's my body telling me to run longer lol