Well in that case it hurts because the nerves on your tooth are probably exposed and air and food are getting to them, which, and I'm sure you know this, if it's not fixed, will cause a cavity and more pain. you can see a dentist during pregnancy. they'll do most procedures.
@arijane316, the reason I have a tooth ache cause I have fill ins and I was dreaming of eating lol and I took a lil peace of the the fill in out of my tooth