Under arm bulge - is it a fat tissue or axillary breast?

Hello doctor Im 32 years old .three months back I stopped feeding for my sonwho is 1.8 months old. last month I had a pain in left underarm. I noticed left underarm and right underarm.right underarm is normal but left under arm looks bulged. i put some ointment and the pain has gone.My question still I have that bulge in left underarm .when I put my left hand down I feel like faty tissue ..can you explain what does that mean.when I touch that its soft.