I had terrible acne as a teenager and young adult and had it mostly under control all through my twenties. Then my skin loved pregnancy, I never had so much confidence in all my life, I was totally glowing.
Now I am back to horrible cystic zits, meaning big ol ones, on my jaw line and neck. I went off the mini pill to see if that would help and it didn't, so I am back on cause I am paranoid of another pregnancy and its the most reliable bc method for me. I looked up acne medications and breastfeeding and most topical prescriptions are okay to use, if I am remembering right. I checked out kellymom awhile back. I think it would be best to use an antibiotic topically than orally if it works. I have just been reluctant to go to the dermotologist cause nothing ever worked for me when I was younger so I am doubtful it would work now. There have been threads on natural alternatives, I think there is a long one in the Teen section if you search there. I have heard good things about proactiv but its expensive and it appears to be just benzoyl peroxide which doesn't work well for me on its own.
I use St Ives Apricot scrub and Aveda exfolient (its spendy but lasts a long time). Both of these remove the dead skin cells that clog me up. That is the best routine I have found. Benzoyl dries me up too much in the over the counter creams.
One prescription that used to work for me was Benzo-mycin. Benzoyl perozide and erthromycin combined in a topical cream. I might try that again sometime soon. It kept things under control but not quite great.
I don't know if its related to breastfeeding as I have always been afflicted with acne but it would make sense in terms of hormone changes.