I was lying on my bed on the top of the covers for 20 minutes and felt an itch on my back. I scratche it several times and when I got up I looked in the miror and saw three bites. I found a few small black bugs(smaller than a pin head). What can they be? With a magnifing glass they look like tiny beetles or spider mites. What can they be and where do they come from? How do I get rid of them? Thank you.