What could be causing sharp (stabbing) chest pains if my heart is healthy?

I have been experiencing sharp chest pain (left side only) on and off for the past few months.  I finally decided to see a Doctor because it was occuring more and more often.  I had blood work done, an echocardiogram and an electrocardiogram.  Everything came back normal and the Cardiologist said my heart was in perfect condition so something else was causing the pain.  I have high blood pressure but in the acceptable range and no other symptoms other than the chest pain.  Sometimes it lasts just a few minutes and other times, like today, I've had it for almost 10 hours now.  Any ideas would be greatly appreciated as I am concerned that my Doctor may just dismiss since the results from those tests all came back good.  Thanks!    

[Encephalomalcia]

See a chiropractic to see if your rib or ribs are out of alignment.  This cause cause sharp stabbing pain.  

[Free1Day]

Was there blood work up done that included testing for  pneumonia, mrsa etc. Also, any chest x-rays of your lungs performed?