Suggest Remedy For Red Blotches In The Arm

I have a small bite on my arm. It started just as a pin prick which itched like mad. It then turned into a bit like a gnat bite (red and slightly raised). Then the swelling went down but it still itched and now it is back to the pin prick but with a red blotchy slightly raised ring round it. Any ideas what this could be? I am assuming it is not anything too serious as I have had it for two weeks already.