Should I Be Concerned About An Intermittent Aching In Left Ribs?

I have a dull aching pain below my left ribs. The first time this happened it lasted 45 minutes and I went to emergency to get checked up for a heart attack. The doctor found no signs of damage to the heart and they ruled out a heart attack after various tests were done, including blood tests, x-ray and a stress test on my heart. All these tests came back negative. The sensation came back again and its been about a week. I was watching the Lakers game while it happened. I feel a sharp pain off and on. I have since taken ibuprofen and am not feeling pain now, but I m concerned at what is making me feel this way. Please advise. Thank you.