What Causes Severe Pain Under The Arm And In The Chest Area?

I have been having a shooting pain, in a spot under my right arm and out to the front of my chest on the right side. I would get a jolt of pain and then nothing. It is not a crippling pain-more of a jolt. It started out happening once every 20 minutes to an hour. I had this off and on for a few weeks. A few days ago the shooting pain became more frequent - a couple times a minute. After the jolt of pain, which lasts only about a half second or less, then I feel fine until the next jolt. This pain is always in the same spot. Last night, I woke up and the pain was a more constant ache in the same area, under my right arm, to approx. my right nipple on my chest. I also felt like I had pressure or bloating in this area. I don t have a fever. My pulse is regular and about 65 beats per minute. I do have an appetite. I m 67 years old.