Until my first was born, I thought teeth didn't come until 6 months or so. However, both my older kids had teeth coming through at about 3-4 months. Micah (10 weeks - born 1/23) has had a bump at his bottom right gum for a week or two, and it's getting bigger, and he's drooling & I can tell it bothers him (at least it appears that way), but I haven't seen the white yet.
My mom said I had my teeth early, and I've talked to many moms who've had the same experience, including a friend whose baby was born WITH a tooth in! Crazy, right?
Hope it's not bothering your LO too much!