Lump under the breast noticed two weeks ago

Dear Ask The Doctor: I have a knot about the size of a egg on my upper left side just under my breast......its like its almost on my rib cage.....i noticed it about 2 wks ago and it doesnt hurt if im not doing anything but if i cough or if im in bed i cant lay on my left side not on my belly.....it doesnt seem to be getting any bigger but the pain is starting to hurt a little more each day.....what do you think?

Dear Angie: I strongly recommend you to make an appointment as soon as possible with your Gynecologist to determine the nature of the lump and proceed with the right treatment option. Because a lump in or under the breast may be a benign fibroadenoma, cyst, pseudo lump, or something more severe, in any case you will need to get done a mammogram, possibly a fine needle aspiration and of course X-rays to determine if the lump is related to the breast or comes from the ribs.