Have had stomach pain for past 2 weeks that feels like flutters on the left side under rib cage along with chest pain and back pain. What could it be?

More than 1 problem. The stomach pain is most likely caused by stomach pain. But the flutters are due to irregularities in your heart rhythm - most often in your age group: premature atrial beats (or contractions). You can feel better by avoiding caffeine, nicotine, alcohol, and getting plenty of sleep and trying stress reduction techniques (like yoga or TM). IF that fails, there are meds that can help.