What Causes Rib Cage Cramps And Stomach And Abdomen Pain After Thoracic Surgery?

I had thoracic surgery last August to remove a tumor that grew behind my sternum from my thyroid. I have since experienced several incapacitating cramps right under my left rib cage that radiate down to mid abdomen my doctor can not explain these. I can relieve them with holding my breath but most times I must stand up and raise my arms. They leave my weak and light headed and I am not able to eat if I drink water my stomach hurts. I have been checked for cardiac problems and they come back negative. Female, 49, 200lb,