Going back to pumping

I stopped pumping at 3 months because my baby won’t take the bottle. He was fine from 1-2 months but refuse breastmilk in a bottle by 2 1/2 months so I have been exclusively breasfeeding him. I’m thinking of going back to pumping because I feel like he isn’t getting enough milk from me now that he’s 5 months but I feel like my milk supply has dropped. Any advice on how to go back to pumping? Supplements, food, or pumping schedules I should stick to?