What in the world is biting me?

Every few weeks I spend the night at a friends house. On those occasions I sleep in her bed. Almost every time I wake up with several bites on me. These are very itchy and inflamed bites, usually there are 4-5 of them in the same area. Once it was my left foot, another time it was my right leg. Once it was my eyelid only. Most recently it is my right wrist and hand. She never has any bites and she sleeps in this bed 7 nights a week. I have her paranoid now about the possibility of bedbugs, although we can't think of how she would have gotten those. It has only been happening since Christmas in the dead of winter in the midwest. Could it be mosquitos, or chiggers, or spider?