I feel a lump under my right rib cage, i have also felt a dull pain there for about a month. any idea what this could be?

Possible hernia: A hernia is a tear in the abdominal muscle. If you have one on your left side then it would show up as a bump in this area and might feel like a pulled muscle. Hernias need to be repaired surgically. Please have an evaluation by your medical doctor to determine what is going on and best course of treatment.

See your PCP: Some conditions like lump under the rib cage require further assessment and your primary care doctor may schedule a follow-up appointment or refer you to a specialist to determine a diagnosis. See your PCP for evaluation.