Lower milk production

My daughter just turned four months a week ago and about a two ago I noticed my milk decreased a significant amount by more than half. I talked with my doctor and she said it could be a hormonal thing or due to the fact I have pcos but to just continue pumping, nursing as I am. I have been having to supplement with formula, which I'm not against, it's just hard when you have a plan to breastfeed. I've been trying fenugreek, lactation recipes, pumping more often and nothing seems to be working. Has this happened to anyone before? Has your supply gone back up? It's so frustrating.. I did nothing different for my milk supply to decrease and I am trying everything to increase it back up but nothing seems to be helping. Any advice or experience would be great thank you!