Platelets are a component in your blood and their job is to help make clots when you hurt yourself. When you do not have enough platelets in your blood, your blood cannot clot properly thus causing easy bruising. Though usually platelets are normal in cases of anorexia nervosa, your platelet count can be lowered if you are deficient in certain nutrients.

You can try fixing this problem by taking a prenatal vitamin because that is rich in folate, vitamin B12, and vitamin K.

 

do them on your bed on top of (or under depending on how cold it is) your blankets.

 

Use a mat. The combination of your bones pressing into your skin, without "padding" (even at a normal weight, some people just have "bony" backs, meaning that's just not where they carry their weight, so this can in theory happen to anyone), and a possible iron deficiency are probably to blame (Iron deficiency anemia causes you to bruise easily).