I pumped for 4 months, until my DD was able to breastfeed. It sucks, I know. I totally sympathize with you and totally understand what you are going through. You can only be away from your pump for 2-3 hours, and then your supply begins to tank and you think you have nothing else. Not to mention everyone around you keeps telling you to just make things easier and switch to formula. Ultimately, you have to decide what is best for you and your baby. Remember, too, that stress affects your supply!! It's like this vicious, self-perpetuating cycle! Moms who pump deserve a special award in heaven!! No one truly understands the sacrifice you make to pump.
When my DD came home, she was almost exclusively fed EBM in a bottle. Breastfeeding just wasn't going so great. I truly wanted her to be a breastfeeder, but there came a point when I almost threw in the towel. It was just too stressful. Then, because she was so colicky, we began to co-sleep. I'd also offer her the breast when she was worked up because that made her calm. Well, those two things made her switch to the breast!! It totally freaked me out because now there was no accurate way to measure how much she was taking in. And, you know after being in the NICU, everything is about measuring! I hired my own lactation consultant (one not associated with the hospital) and she helped us totally transition to the breast. However, I like to say that none of this was really my doing. My DD was so determined to breastfeed, so I feel like I am blessed.
Just realize you have to make the right decisions for you and your baby. In the end, no matter how many times I entertained the idea to stop pumping, it just never felt "right" to me. You have to decide what is right for you and your family and what makes you and your baby happy. It's not easy. But, then again, if it was easy, everyone would be blessed with preemies!