breast lump

hi i am 16 years old, and i have just noticed a small marble sized lump on my right breast, around the armpit area. But, i just noticed it right when i started my period. i usually get swelled painful breasts when i start my period, but i have never felt a lump like this. The lump is painful when i touch it and it is also bruised and reddish right above the lump,and i am just worried it could be serious. i would gladly except anything anyone has to say

thank you