Erection problem

Patient: Dear sir, i m 21 yrs boy . my weight is 95 kg and i smoke a lot . and i masturbate 2 time in a weak. i have sex with girl only 1 time in my life , in that movement my erection was very week , so week that even i was trying to put condom but i cant , coz penis was bending down , sexual desire was there but erection was very week ,, i cant do intercourse coz of that . plz advice me what to do.