Trying to stop bfeeding but Im prone to plugged ducts-help me wean!

Journey33

Can someone please shed light on this process? I've had some health setbacks and need to stop bfeeding. Im really bummed ab it but it;s the right thing to do at this point.

Because Im prone to plugged ducts-that have turned into mastitis twice Im not really sure how the best way to do this is. 

I pump every 3 hrs for 20 mins.  Im afriad if I dont completely empty or go longer than the 3 hrs that Ill clog up again so Im always telling my body to make the same amt of milk.

Ive tried cold compresses between feedings and sage tea (only one cup and I started this only yesterday) 

At what point will my supply change/diminish? 

I know some people would love to have this problem, but is there anything else I can do to dry up supply?