From the area of the body it is biting you on, and the fact that you can't see them, almost sounds like bed bugs. They are extremely small, very hard to see. I would suggest taking your sheets up and lifting up your mattress to see if you can see them. I think they generally look like tiny bits of black pepper. With regards on how to get rid of them, not sure. I would try googling "bed bugs" and see if this sounds like them to you. They should have suggestions on how to get rid of them.