hello. i'm 18, male. recently i've had some troubles with my erection while masturbating. the erection is not as stiff as it used to be and after the ejaculation it disappears very fast. a year ago my erections were so hard that it actually hurt when trying to bend the penis up or down, nothing like that now.

i'm afraid that the few years of smoking have damaged the blood flow to my penis, recently i've quit. so here's my question: will quitting improve the blood flow again or have I damaged my erection permanently. is there any diet, exercise or anything that helps to improve the situation?