Looks like hives.

Edit: Also, if you haven't had systemic anaphylaxis by 20 min after the appearance of hives, the chances of you actually having a big reaction is fairly low (but not impossible). Benadryl works really well as an anti-histamine, and you can put some hydrocortisone on the itchy area if it bothers you a lot. Ice also helps to reduce swelling and inflammation.

Edit 2: I reread your post, and you say the inflammation only occurs after scratching. Does it itch, or are you just scratching it to see if the bumps go away?