Hey dude,
I'm 19 myself and I used to smoke pot daily (ages 15 to 17). Let me begin by telling you how much better I feel...You will one day realize that pot sucks and it's really expensive...You dont need to smoke and get high all the time. You will be able to manage your time better, improve your mental and social skills, improve cardiovascular health.
Everytime you smoke a joint, you smoke the rolling paper also...Therefore you're inhaling many of the chemicals found in cigarettes...smoking with a bong is obviously the ''cleanest'' way to smoke, but the marijuana itself fills your lungs with tar. There is a thin membrane-like substance on the inside of your lungs...it's tar. Also, your alveolus' get clogged up, which makes them less efficient at absorbing oxygen. Basically, your entire cardio-pulmonary system is affected. You wont need to worry about cancer because marijuana is known to actually reverse cancer cells from multiplying (yes, marijuana has excellent medical properties)...
The more crap that you have in your lungs/heart/arteries/veins/capillaries...the less efficient your pelvic cavity will be at pumping blood into your dick.
Alcohol, amongst many things, reduces your testosterone levels. Less T = less gains. If you have to drink, go for red wine.
I'm not a media-influenced marijuana hater. In fact, I hate the image that the media creates about marijuana. I've smoked a lot of it and this is my personal opinion. Pot sucks. It's really cool when you start (for the first 4-6 months)...then you dont get the same feeling anymore. Eventually, you only get doped out. Quit smoking and everything will clear up (in your head, lungs, veins, etc)...Trust me.
What routine have you been on?