What kind of bug bite is this?

I have what I ume to be a bug bite on my inner thigh. It's a blackish-purple lump about the size of a dime, it's really sensitive to touch, the lump itself is very hard, but no visible bite marks. I've been feeling pretty crappy, i.e. feeling really warm, clammy, chills, constant headache, difficulty swallowing, back muscle cramping. I've been feeling like this for five days, and I noticed the lump three days ago. The headache is gone now, but the lump's still there. Can anyone tell me what I have? Thanks