It's called PE (premature ejaculation). The treatment sometimes includes antidepressants. Please talk to your doctor about the down sides to the drugs... I know of a guy that now has ED from taking the drugs too long.
Erectile dysfunction means not being able to get an erection which you clearly can, so you are good. That you have ejaculation after 5 minutes with porn isn't a sign of ED and that you then can't get hard right away isn't either. I wouldn't worry.