Re: Getting back to exclusive BF
You can definitely get your baby off formula supplements! Lots of moms relactate, and you're actually in a great position to do it because you still have milk. You won't be starting from scratch.
My Mom needed to wean my sis when she was 3 months old due to some medical issues (hers, not my sister's). Mom never had any luck expressing milk, and when she was given the go-ahead to nurse again after 3 months off, her milk was totally gone. By putting my sis to the breast before giving a bottle, she was able to rebuild her milk supply and phase out the supplements. She went on to nurse my sis until she was 18 months old. Perhaps that's a good way to start your journey: nurse your baby before offering a supplement.
You can also try supplementing using a supplemental nursing system (SNS). A SNS is useful for 2 reasons: first, it teaches your baby that all his meals come from the breast, so he stops wanting the bottle. Second, your baby will stimulate your milk supply even as he feeds from the SNS tube.
How much water should you be drinking? Only as much as you want. Some people tell you that you need to drink X amount of oz of water when nursing, but most of the advice I've heard is to drink to thirst.
Regarding the pump: have you been to see a lactation consultant? Perhaps she could observe a pumping session and see if you need a better/different pump or breast shields in order to get maximum milk removal.
Keep up the good work, Mama! If you are determined, I have no doubt you can get a full supply back.
Coolest thing my big girl said recently: "How can you tell the world is moving when you are standing on it?"
Coolest thing my little girl sang recently: "I love dat one-two pupples!"