I've been with my girlfriend for about 6 months now and I have had no problems staying hard for long periods. Only recently since I got heavily into smoking I seem to have problems staying hard. I'm a heavy set guy (300 Pounds) at 17 years old might blood flow be an issue? Before when I was errect I have a large vein in my penis which grew really thick upon an errection and now it doesn't seem to fill at all. She is in no way unattractive to me. Please help?