Hi momma...
How old are you?
How often does this occur?
Can you seek help from a doctor WHILE it's happening? That's often the best way to get a diagnosis.

Are you short of breath, or do you get short of breath after moderate exercise? Have you been involved in a traumatic event recently?

I also suggest seeing a doctor asap.

I am 27 and this happens once and awhile but it has happened more lately. 2 times this week it was in the rib cage under my left breast. Last nights episode would not go away like the one earlier this week so I had to try to sleep it off. This morning I woke up witht the same pain and it got worse. I finally had to force myself to breathe in deeply to get that "popping sound" and then it finally went away. It seems to happen later at night so I could to the ER while it is happening but I am going to make a Dr appt. I just do not like the Docs in my area. They are quick to dismiss everything as nothing. I have not had any recent injuries or trauma. I do get short of breathe sometimes but I have a mild asthma. Thank you for replying. I just wanted to know if others have the same issue and what they were told it was.

If it were a musculoskeletal disorder, it could be a cervical rib. Could be a congenital anomaly in the diaphragm. Do you have any adjoining pain in the arm?

Try and feel the ribs, first on the unaffected side and then on the affected side, and see if there is any difference.