I have also been experiencing pain on the left side of my body for about 3 weeks now. I finally went to my PCP yesterday after my left forearm and hand swelling up. I was told it is more than likely a compressed nerve in my back since it involved both my arm and leg. I have also had numerous tests on my heart already so that maybe why they ruled out anything cardiac in nature. I have to take anti-inflammatory meds for the next 10 days and if that doesn't work to go back to her and see if a MRI is is in order. Good luck to you and I hope it is nothing serious.
You need to get to the ER NOW. It's probably something simple, but it is one of the classic symptoms of a MI.