I got bitten two days ago on the arm. I think. I was working outside and looked down and it was bleeding, I didn't catch or bash it that I know of.
It's been itching like hell ever since and now has swollen up and it got and hard.
Going to the doctor on a weekend will cost me a small fortune (not in the UK) and it's 2 hours each way (please whatever wait the ER will have.)
DH thinks it's nothing and I shouldn't be worried but he's no good bloody judge, he's one of these people that doesn't go to the doctor until he's half dead or a limb is falling off. 
Pictures included. I'm assuming it was a spider bite as a red ant or similar would have hurt more at the time.