Non Rash Red Bumps Everywhere?

I came home from college for the weekend and woke up the next day with red bumps all over my legs, a few on my hip, and one on my wrist. They itch like crazy. I thought they were spider bites because my room is known to have a lot of spiders in it (we once found two spider nests in the corners of my closet I never use). There were 15 on one leg, 5 on another, 2 on my side, 1 on my wrist. Over the next week they started getting smaller and are almost gone. I would have left the situation at that because I slept out on the couch for the next week and had no further problems.. until today. Today I find about 10 more of these big red bumps on my side. They itch as well. I haven't slept in my bed at all since the first day, so I don't it was spider bites. One of them is huge, about the size of a nickel. The bumps just seem too big and spread out to be a rash, I have no known allergies, and we do have dogs. The thing is, everyone in the house has as much contact as I do with the dogs, and they show no signs of bumps or anything. What could be wrong with me?