Problems with my erections

This is my first time ever writing on a forum... Well i have been having problems with my erections. I have morning wood but i feel them not to be as hard as they used to be.. when i do jack off if i dont continue the stimulation i lose erection almost instantly not to say i dont get one but that is just not ryte from wat i remember as it feels soft. The first time i realized this was almost 7 months baq but i was on heroin and wasn't much concerned as i knew it was a consequence of my consumption of that drug however i am clean for over 5 months noe and the problem was gone as i cud easily maintain an erection till 3 months baq and i first noticed this problem when i was having sex and was having a soft erection but dismissed it due to consumption of alcohol. Some other information about me is that i am 24, slightly over weigh (working on it), chain smoker, totally stressed out as i am trying to find a job. basically there are so many things wrong that can cause my problem but for curiosities sake i had to post my inquiry here and ask opinions. I asked and talked to a friends father who is a gynecologist who told me to stop smoking and work on my weight but i have been unable to stop smoking as i am addicted to it. What i want to know is that if anyone had a similar experience and wat they did so i may follow in their foot steps. I also have a visible scar on my genitalia which was not there before and seems like a discoloration that is white in color. This scar appeared at the same time approx that i started having these problems but i remember once when on heroin that i tried to jack off and due to not having a erection i sorta forced it and hence i believe this scar appeared but didnt make much of it until this problem became real.