Lumpy boob

[Naboo]

Hi, Just wondering how long it takes for your boobs to go back to normal after you finish breastfeeding. DS last feed was last Saturday. I gradually reduced breastfeeds until that final feed was only really quick both sides. Since then one boob (which was DS prefered side) has had a lump and wont go away. It doesn't hurt, and I massage it down in the shower and squeeze a little out but it still wont go away. Today it seems abit worse and harder. When I hand express, it still seems like there is alot of milk there. Should I just leave it alone now and will the lump go away? I'm scared that I'll get mastitus. Or is this normal?

Thanks!