I would suggest you make an appointment ASAP with a dentist, inform your obgyn of the issue and ask him for clearance of dental procedure, which will include a few x-rays (low radiation dose digital), anaesthetic (without epinephrine) and antibiotics. The dentist will probably call then obgyn, once a diagnosis is made. The main reason we do not treat in third trimester is because of comfort of patient. We will treat women during all trimesters for emergencies. Good luck, perhaps your baby will become a dentist!

Alan Howard