How to increase my milk supply?

I dont know if my LO is full with my milk as she falls asleep after 5 mins of feeding n then she pulls onto my nipple like my nipple is a chewing gum....its too painful when she does that. I do top up with formula but sometimes I just dont know if she is feeling well.

I really want to increase my breast milk. But as soon as I sit to pump she wake up which is after an hour or two of sleeping. I honestly would really appreciate any advice as to how to increase my breast milk.