What Causes Recurring Sharp Pain In The Left Corner Of Ribcage?

Recently I have been having pain, sometimes sharp, in the left corner of my rib cage. I attributed it to our relatively new, and very affectionate Poodle-Bischon mix dog (15 pounds) jumping up on my lap from the left side of my recliner for me to hold and pet him. Sometimes he catches me off-guard. However, minutes ago, I was awakened by pain, which is intermittent, and decided to research the problem I am having. I am very obese (300 pounds 5 9 ) and have Type-II diabetes, A-fib, high blood pressure--all under control with meds. For 3 days I have put a small cushion at the spot to protect myself the dog s action. In this time, too, I noticed that when I stretch out on the recliner, I experience discomfort from pain on the left side and sometimes, it seems, a little on the right side. I have surmised that the fat under the rib cage is a factor, but that I may have a bruised rib on th left side. What do you think? Also, I had started exercising (stationary bike, light weights, etc. to the extent that I can, having had two knee replacement surgeries and needing my right kneecap to be replaced. Should I keep on exercising, as this does not seem to aggrevate the problem?