Pain in chest/sternum area when exhaling

Hi there,

About three weeks ago I started to feel pain in my chest whenever I smoked pot. I've smoked pot for a year now with no effects to my health. After about a week I started to feel the pain all day, but very mildly. The pain is like someone is pushing or squeezing my lungs or heart when I breathe, I'm not sure which. It has gotten worse since it started. I've smoked pot a few times since it started hurting to see if it would take the pain away, and when I do it has made the pain a lot worse. Also when I smoked, along with the pain when exhaling, I felt random sharp pains throughout my chest. When I lay flat on the ground it generally feels easier to breathe without pain. But not completely.

Some things you should know are: I'm going through depression so I'm on antidepressants (Welbutrin) and have been for just over a month. For the last 4 months or so I haven't been eating well or eating enough, due to the depression. I'm 130 pounds, 18 years old. I don't smoke cigarettes and I rarely drink alcohol. Up until the pain started happening I smoked pot pretty frequently. Once a day, at night so it's easier to fall asleep. Now I've stopped because I'm really worried about this. If ANYONE has had similar symptoms please tell me if you have any answers. I've had a blood test, chest x ray, and another test that I forget the name of (they put stickers on my body attached to wires, that monitored my heart or something) and I'm waiting on the results for all three. Thanks for any help anyone can offer.