lump under arm pit

im a 29 yr old women preety healthy i smoke about 10 cigs a day about a mounth ago i found a lump under my arm pit it is on the left side and just above the pit it is visable when looking in the mirror it does not hurt and there is no skin irritation my nan has just had a brest removed due to breast cancer which concerns me i havent made an appointment with my doctor i was just hoping it would go away. im a single mum with a full time job so life very stressful any advice would be good thx

[Cleveland Clinic]

Dear emma182:  Lumps under the arm could be many possible things.  Without evaluation, it is impossible for us to speculate on what this might be.  Since it has been a month and the lump is still present, you should have your doctor evaluate it for you.