I have one of my breast is enlarged and i had it checked and they said it was not cancer, it started to get bigger. what could this be?

Could be normal: Some times one breast could be larger than other breast ( or smaller than other breast how you want to say ) , if your doctor checked and said it is normal , then most likely it is , but however you want to make sure , take a second opinion and follow the advise, if tests are recommended . In some needs cosmetic surgery good luck.

Asymmetry: There is always some asymmetry between the breasts. If you are concerned you should alert your friendly primary care doctor and perhaps have an ultrasound.