Baby is drawing lots of vitamins and such from you and one thing the baby is taking alot is calcium. Tooth decay or bleeding gums are pretty common. It will usually get better after delivery but also remember to keep your calcium intake up. But I think if you are in pain, you should go see a dentist. You don't want it to spread or cause any further problem to your other teeth!
go and see a dentist lo. but make sure u highlight to him/her that u r pregnant so they will take precautions. i experience bleeding gums since pregnant. i did call up my dentist when my dental appt was due n i was just pregnant. they advise me to see them only when i'm 5 mths pregnant as they say bb is more stabalized then. well... have yet to make my appt but will be making soon. read in magazines n books that our oral hygiene is very impt too so should see dentist.