It should never feel bad. The bad feeling is probably your body’s way of telling you you’re overdoing it.
Jelqing should be invigorating. If you do it so much that it screws up your erectile quality you’re probably definitely overdoing it. I used to hang weights until my unit was as limp as a noodle. All it did for me was toughen it. Yes I probably could have towed a bus with it, but that’s not the object of the exercise. The idea is to stimulate it enough to make gains, not to toughen it up. I used to try and deliberately condition mine so that I could hang heavier and heavier weights, because I thought higher weights would make me gain faster, but all it seemed to do was strengthen it making it more difficult to stretch. It truly did seem to become conditioned and strengthened to cope with the added force. A conditioning and strengthening that seemed to prohibit growth.