Particularly "Nursing is a supply & demand process. Milk is produced as your baby nurses, and the amount that she nurses lets your body know how much milk is required. Every bottle (of formula, juice or water) that your baby gets means that your body gets the signal to produce that much less milk."
I found this tea to be quite helpful.
I was in your shoes, OP. It's called the top-up trap. The more you supplement, the less your body makes. It's a vicious cycle. If bub won't sleep or settle, put him to the breast. Your breasts are never empty- ever. They may feel like it but they're not. They keep producing, constantly. Getting your supply back up is hard work, especially if you've been supplementing for a while. I would definitely recommend you look into a supplemental nursing system and start reducing the top ups- how much are you offering? At one point my DD was taking 80mls after each bf and I managed to wean her off them and get my supply up. She is still bf at 20 months I started by cutting it down to 60 ml, then the next day 40ml, then the next day only every second feed and so on. You have to compensate by breastfeeding a lot but within a week or two your supply will meet the demand without the excessive feeding sessions. Be aware though that periods of fussiness and prolonged feeding are normal in babies, especially evenings. Breastmilk is also digested much faster than formula, so feeding IS more frequent anyway- around the clock in most cases