Blood Blister Under My Breast

My breasts have gotten much larger when I started taking Birth Control. And since the summer  I have had these heat bumps under my right breast. They start off looking like a heat bump and then they look like a blood blister. I have gotten a new bra and started wearing powder and I try not to get that hot so I wont sweat. But they keep coming up. Only two have looked like a blister and the rest look like heat bumps. I used to break out between my breasts when I was in sports. But now its below my breast.  I dont know what else to do ... and if it could be cancer.

[chellybeans]

it is probably not cancer, but  a yeast infection. go to a dermatologist so they can do a culture