I just had a bout with "itch mites" a very tiny little nympth thing (I think larval stage of some kind of gnat) that lays it's eggs on pin-oak leaves. We have one big tree, a pin Oak! I had no idea. Anyway, they float or jump down from the trees, or carried also most anywhere by birds, and they bite. Millions of them can come from one tree. The bites are almost exclusively on the back, shoulders, upper arms and chest. Feels like a spider bite, very burning and itching for about a week, my bites looked an awful lot like your picture. They are unlike chiggers, which burrow, these just bite, like a spider. They look like a tiny pin-head sized tick.
Nebraska had such a bad outbreak of them in 2004 they had to call in exterminators into their parks, etc.
The Hartz pet supply company makes a very good home spray for fleas and ticks, called "Ultra Guard", it killed those little guys very quickly. The itch lasted a week however. Ultra Guard may work on your mattress and carpets as well for what ails you.
There are also bug-proof mattress/pillow covers you can buy. (pretty cheap) They just die if they can't get out to eat!! I'm getting grossed out all over again just thinking about this! I think I picked them up when I filled my bird-feeders.