What Causes Discomfort In Chest?

Hey, I am a 64 year old male, About 4 weeks ago I noticed a little discomfort in my chest when I went to bed. The next night the discomfort had turned to pain and I noticed a large lump under the skin about half way between my sternum and right breast nipple. The next night I woke up in extreme pain in the same area caused by me coughing. This went on for about 2 weeks with the pain getting worse and worse, so bad was the pain that I was actually moaning. The pain was unbearable when I coughed or sneezed or changed position in bed at night. I went to see my doctor where they gave me a series of x-rays from different angles of the infected spot and they also gave me a sono-gram of the infected spot. The results were negative so he scheduled a CT/Scan which the doctor who read the pictures said it looked like a muscle but the pictures were not defined enough to make a diagnoses. My doctor is now trying to get my insurance company to authorize an MRI. This lump is about 1-11/2 inches wide from top to bottom and about 2 inches in length, it is about 1 inch from my breast bone and is in line with the nipple of my right breast. What could this possibly be? It just started hurting one night and has gotten worse. Never had a lump there, and out of a clear blue sky it appears with no apparent injury? What could this possibly be?