Itchy white welts on skin that last 1-2 hours (re-post with details)?

For the last month or so, I have been having a weird skin reaction. In fact, I just had this happen about half an hour ago. I got out of the shower and about half an hour later,I was sitting on my bed and my upper arm started to feel itchy. After scratching it, I noticed a long white welt that resembled a mosquito or ant bite. However, I know that it is not a bug bite because I was not bitten and it feels like a welt--stinging as if I have been slapped with a rubber strap or something. Suddenly, that one long white welt grew into a much thicker welt, surrounded by smaller ones that look like bug bites. Now the area is red, hot to the touch, and stings, but the itch is not as severe and the welts have kind of congealed into just one thick white welt. As I've said, this has happened to me about five or so times this month on different areas of my body, but it always starts the same way: An extreme itch that is accompanied by welts and redness. What could this be? The welts have gotten better now, but should I visit a doctor? Could it be some kind of allergic reaction? Thanks in advance for any answers :)