because you've been experiencing symptoms for over a month and because the symptoms seem to be getting worse i'd suggest you make an appointment to visit your primary health care provider for an exam. it doesn't sound like this is too serious in the medical sense but it's serious in the sense that you're having bothersome pain. this definitely warrants a check-up. take care!
i have a dull soreness underneath my armpit on both sides. been close to a month now that i have felt this. . sore to touch and not very sensitive otherwise but i can definitely feel that something is up. initially was just on my left side but has started becoming apparent on my right side now as well. 6-8 inches below my armpit and closer to the back of my torso than the front. these sore spots are not visible.