I think i've fractured a metatarsal. what should i do?

See your doctor: Problems like these can only be correctly handled by your doctor in person. He/she needs to listen to you, perform an examination and possibly run labs or other tests. That's the only way he/she can find out what's going on and what to do about it.

See a podiatrist: A podiatrist will examine your foot, take some x rays and begin treatment. If it is a fracture with little or no displacement (still lined up), you may just go into a flat soled post-op shoe for a few weeks with some pain medicine. If it is the 5th metatarsal near the base, you might need a fracture boot or a cast. If it is displaced, surgery may be recommended to line it back up and fixate it.