I suffered from mastitis. Was prescibed amoxycillin which got rid of the horrible flu like symptoms but never really got rid of the painful lump in the breast. (Made it better though so I carried on breastfeeding). Got mastisis again, and again prescribed amoxycillin. Again, cleared up the flu symptons but not the lump completely. Later on, lump turned into horrendous breast abcess and I ended up via A&E to the breast clinic at Kings. Along with draining etc, they prescribed flucloxicillin, a much better antibiotic for mastitis. If I were you, I would go back to GP and ask to change to flucloxicillin straight away. To note, make sure your iron levels are ok, and you are not suffering from anaemia at all. Being low on iron can also not help with mastitis and getting over it. mastitis is so horrible and exhausting when you have a new baby to cope with too. Hope you get better soon.