What mold is this? ?

Question

Mold keeps growing on one wall of my bedroom, behind my bed and the wall at the bottom sounds hollow when you knock on it, and its coming away if you pick at it... 

Answer 1

dampness mould 

Answer 2

you have a leak in the roof or the gutters need cleaning .  . 

Answer 3

is it an outside wall?  a bed should NEVER be against an outside wall ..that looks like penetrating damp ..but if behind a bed lack of ventilation and bed position is probable cause