This doesn't sound like breast cancer,since this disease is almost never associated with pain and cancer would be very rare in males particularly at your young age.What you have is probably due to a benign condition called Gynecomastia,which is very common in teenagers and is caused by an imbalance of the hormones estrogen and testosterone,which promotes tissue growth or a painful lump under the nipple area in one or both breasts. Generally,Gynecomastia isn't a serious problem,and sometimes goes away on it's own after a while...but I would advise you to see your doctor for a medical exam,in case it's an infection that would also present the same way and could be related to the swollen lymph node in your armpit
I am sure your doctor will be able to figure out what the problem could be and prescribe an antibiotic if you have an infection.
but the lump is not under neath the nipple its above the nipple on the skin!!!
There are so many possible causes for a painful bumps...The good news is that breast cancer lumps are not usually on the surface of the skin and they are not usually painful.
You might have a pimple, boil, or other type of skin infection. If it doesn't get better in a week or two or if it gets worse, you'll want to have a doctor look at it,okay?
It's been there for like 2，3 months
If you have this lump for almost 3 months,then it's one more reason to see your doctor the sooner the better.
Don't let this go on unchecked for longer than it has already been.
I am sorry if I can't be of more help...We cannot specifically identify anything over the internet.You need medical attention to find out what this lump represents.