How to Up my breast milk supply

Me

My baby just turned 4 months old and I’m having trouble producing enough milk for her to eat. When she was first born I had an over supply of milk I had to pump and I’d get 5-6oz out of each breast but at 2 months old she was dx with Leukemia and we were hospital bound for her treatment and my supply dropped so much! I was wonder if anyone has upped there supply with any supplements? And if so which ones? I’m trying to feed my baby and keep her going any advice would be helpful.