Could scratching lead to infection in Breast reduction in only a few hours time?

On the third day after surgery I began some light scrarching on the left side under the armpit. I made it under the bandaid once. A few hours later, that side was seems a little swollen/puffy but not red and still red/more painful. I looked and there is a maroon blood spot that is not covered by a bandage and some black stuff that stuck to the adhesive. Can i clean and re bandage? Is this getting infected? I have a post op in 3 days.