How long has this been going on? Is it related to any activity or exercise? Is it after meals? Have you done any new activities lately?
Just started yesterday, not related to any activity or exercise that I can think of. Not after meals it is constant. No new activities lately.
It is possible it is a pulled muscle. It could also be gall bladder unless you've already had that removed. Another possibility is an infection in your lungs. If it persists, you will want to get in to see your doctor to check this out. if it is severe, enough to keep you from sleeping or doing normal activity, it merits a trip to the ER tonight. If you have any fear at all that this is related to your heart, again the ER tonight is the way to go.