Bed bugs can leave a single bite, a pair of bites or bite in a pattern. Patterns are caused by an arm or leg that is resting against a seam in a mattress where bed bugs are hiding. Just as a FYI, they rarely bite the bottoms of the feet or face, and concentrate on exposed areas during sleep. Said another way, if you wear tight fitting clothes to sleep (long pajamas with socks over the bottom), you can minimize your exposure.
The bites are an allergic reaction so will vary from no bite reaction in most people, to a collection of bite reactions to a large round wheal.
I've attached a resource that is filled with bed bug bite pics for you to compare.
Simple. Wash your sheets. I promise they'll be gone.
Also to make sure their gone; wash them about 2 times a week.
As written, one interpretation of what you said here is that three is a pair !
Anyway, who says they have to bite in any number ?