I have a sharp pain and feel like there's something swollen under my rib cages (left side and in the middle). it occurs atleast once every 6 months and will last a for a while. is this something severe?

Likely gas: The large intestine crosses just under the diaphragm at that location. In many people it rises on the left side making it a prime location for bowel gas to accumulate in an upright person.Distension of the bowel triggers pain. An abdominal x-ray standing up will often confirm that finding. I wouldn't consider the bad stuff when this can be easily documented.