Worried about Erectile Dysfunction

Patient: Hi i am 17 and im not sure if i have an erection issue or not and if so what i should so about it,sometimes i have a what i would say is a very good erection, without trying to be perverse, it is over 7 and a half inches long,fairly round and it gets very hard and a dark color, but these are every rare(and i would like more) but most times i am barely 6 inches long not very big in diameter and isn’t the “solid firm hard” i like, more of a stiff but bendable, i also have a difficult to extremely hard time maintaining an erection if there isn’t constant or almost constant “stimulation”, so is this Erectile Dysfunction and if so how can i fix it to get the first described erection to be more constant.