Having slight chest pain?

Im 17 years 150 lbs old very active, go to the gym 4-5 times a week 13 percent body fat, recently over the past 2-3 weeks ive been experiencing random chest pain on the left side, i have a faster heartbeat when I run but no shortness of breath, coughing , weight loss, or fatigue. I Can still workout my chest without any or relativley short pain, its on and off and i occasionally smoke marijuanna never ever a ciggerate tho. What could it be and could it be lung cancer ? today i feel a weird feeling on my left side no pain at all though