curious about some chest pain...

I'm a 20 year old male, about 6ft. 2in. tall, and weigh about 185 lbs. I'm having this really weird chest pain. When I stand normally, it doesn't hurt, but when I turn my body sharply, or stretch my back and shoulders in certain ways, I get this sharp sting in my sternum area (more so on the left side). It seems like this started about 2 weeks ago when I started going back to the gym (after not working out for a while). I thought it was just my muscles cramping up or something of the sort, but the pain seems like it's centralized more on the bone portion of my sternum (if that makes sense), rather than my muscle. The pain is sort of sharp/tight. I also recently got over a cold (if that matters). I went to the hospital about a year ago complaining about a hard time breathing, but they found nothing in the chest x-ray. They said it was just anxiety. I do tend to be nervous a lot and be anxious all the time, could that be it?

Please let me know what you think.

Thanks!