so i am 17, and its been around 2-3 months since m facing this problem.3 months ago, I used to have perfect life without any sexual related problem. i really dont know why i went out with some of my friends and they guys have been smoking since a long time. n i tried cigarrete that day again, like it was my 4th or 5th time.while i was smoking i inhaled some extra smoke due to which couldnt exhale it properly and got some kind of bad sensation near my testes. that thing hitted my brain so badly, at that very moment i started thinking what the f**k actually happened, have i turned impotent and stupid stuff. as i was really tensed, i managed to come home it took me an hour. i was really worried. so i thought to give it a try, i watched porn, and tried to masturbate. yes i could get erection. dont remmber how much in % it was. but i got erection and masturbated. i was still worried. and from 4-5 hours it went that way. that night i was so scared, my penis size also got shrinked, i discussed all the stuff with my brother and felt a bit better. still was tensed. those stupid thoughts kept n striking me.after a day, we went to see a doctor,he told me it was psychological erectile dysfunction and gave me herbal medicines, and also told my desire central activity got disturbed. i need to relax. after 2-3 days i started getting erection again. not that good but it worked. n from that day after 2 motnhs, now i could get really good erection, but since past 2-3 days, i 'm getting worried again. n its getting hard for me to get erection and masturbate, i have been masturbating regularly, n even cemen came out from penis. it still comes out. but now the problem is, its taking alot of time for me to get erect, and its taking time to erect too, for it to get hard, and stand properly. i really dont know what to do, :( am really tensed. please help. if you can guide me what to do.