Having had eczema for 23 years, I can tell you the patches that flare up under clothes (breasts, stomac, legs) - are ongoing -- with patches lasting for months, on occasion. It is controllable -- but cannot be cured.
Dear tide: Time will differentiate between the two. If it is eczema, it may be helpful to attempt to identify if something is a trigger for this (new bra?, new detergent? new soap, perfume?). Give it a bit more time to heal totally. Breasts stay pretty covered up so it may take more than a week to heal. Paget's disease is uncommon. If this is still there in two more weeks, consider having it looked at again.