I'm not an expert by any means, but that sure looks like poison ivy (or oak or sumac) to me. It itches like the devil, and it kind of spreads in an irregular pattern. I've used Benadryl spray to help quell the itch, but if that's what it is, it just takes time (and avoiding scratching) to go away.
While this could well be a bite reaction and it is prudent to rule out a tick bite induced Erythema migrans(Lyme borreliosis) despite the fact that this not typical.
It is most important to bring to notice to your physician.
diagnostic process may be delayed if a physician does not recognize a skin rash caused by Lyme disease because it does not have the bull's-eye appearance that is best known to physicians and the public.
It does appear like a bite of some sort because of the red spot in the middle.
It also likes like the poison is spreading because of the red inflamed area around the bite mark.
I would suggest you see your doctor so that he can prescribe you with an antibiotic to kill any infection and also an antibacterial cream.
In the meantime, keep it clean and try not to scratch it as it will make it worse.
You can try applying natural live yogurt if you can't get to see your doctor soon. This will cool down the itching and also draw out the inflammation.