Definitely follow up and make sure it clears completely - ask your dr for an ultrasound and a fine needle biopsy if it doesn't... I had a persistant lump (well I thought at the time that it was just a recurrent mastitis/blocked duct) which came & went but eventually turned out to be a tumour. So, don't be worried (chances are it's mastitis related) but if it's nagging at the edge of your mind then definitely get it checked out thoroughly.