Can't maintain the semi for more than a number of seconds
It is very frustrating. If I masturbate it for a little while, it goes beyond the semi required for jelqing(and jelqing actually hurts in this situation), and I wait until it subsides and then jelq, but then the semi itself quickly subsides. So the jelqing session is just a session of constant losing and gaining the erection, jelqing for a few seconds while it subsides, then getting it back up, waiting for it to get to semi-erection, jelqing for a few seconds, then it subsides etc.