Ouch Laura.
Dunno about mastitis as i havent had it before - it could be blocked ducts? I think mastitis is accompanied with flu like symptoms where as blocked ducts is localised pain!

either way the only cure for both is you have to keep draining them for it to clear!
A/biotics also are given for mastitis
keep hand massaging and getting bella to suck her little heart out to drain those boobies- you can have some panadol or panadeine to help with the pain and that might give you some relief whilst you drain them!
let the shower hit where it is sore to massage them and use your hands to push the milk free towards your nipples!

hang in there hon- !!
to prevent it as much as you can from happening again- keep the massage in the shower up daily at least! unblock them before they have a chance to totally block up again!

mwah and ouchie