I Have Had Upper Stomach Burning Fot Three Days, But

I have had upper stomach burning fot three days, but now my stomach feels like there are rocks in it and I have a feeling that it is being pulled down towards my pelvis. I feel nauseous, and today woke up with diarrhea. I spoke to a pharmacist on Saturday, and he told me to buy Nexium, and antacid for the burning, so I have been on that since Saturday, and the horrible burning started Friday evening. I also have heart palpitation and find it hard to breathe deep. I cant lay down or sit for extended time, due to the pain.
Am I taking the correct medicine? I havent any insurance, and Im working in Idaho, not my home town. Afraid to go to ER due to the cost. Please advise.