What Causes Sharp Pain Under Right Armpit With Burning Feeling?

Felt very sharp pain under right armpit last night. It felt like extreme sharp electric prod or stabing the size of a baseball. This went on for about 30 minutes and was very scary. Im 49 with no prior health issues. Went to store and purchaced Bayer asprin 325 and chewed 2. the pain went away and now is just a slight nagging or slight burning in area. also felt a slight aching in left shoulder at the same time. this has also passed. Any ideas? Thank you.