Anyone know anything about spider bites!!?

I have a huge bite on my right butt cheek. It has grown in size since yesterday. Painful and knotted. The bite resembles a nipple, my butt cheek looks like a huge boob! I have.. A buttboob haha. I'll go see a doc tomorrow for it but am a little worried since I'm 6 weeks preggo. Any advice would be much appreciated. Sorry for the buttboob pic! Ponytail holder for scale.