What the heck is this thing?

Lately I've noticed at the front of the opening of my vulva, there is a round, gland-like thing that protrudes slightly from the opening. I didn't really think much of it at first, but it's really uncomfortable to touch, which makes sex very uncomfortable. It also seems to swell slightly when agitated, such as after intercourse. What is this thing? And why is it all of a sudden in my way?...