Blood spots rash under skin on left breast at the bottom and it itches a little. i am scared to death. can this be breast cancer?

Rash: Not likely a breast cancer, more likely a skin disease like eczema, which especially with pendulous breasts may become irritated or infected. First see your pcp or obg for a good breast exam including palpation for masses or nipple discharge. This may just be a skin disease, but should be checked.

Probably not: This sounds more like a heat rash or contact dermatitis and not cancer. However, if it does not resolve quickly, you should see your physician. You are young but inflammatory breast cancer typically presents as a skin redness and inflammation and can progress rapidly.