R.,
It seems like most everyone has said just about the same thing. I have had a similar situation, and my daughter is only 3 months old! I had to go back to work when she was 8 weeks (so hard). I'm a Pre-K teacher at an Elementary school and pumping at work hasn't been as easy as I thought it was going to be. I got to be really bad at it after about 2 weeks, so I was thankful for Christmas break so I could concentrate on building my milk supply back up... I actually learned some new things with the responses of other people, but I was going to let you know that I just sympathize with what you're going through. But don't be too hard on yourself if it doesn't work out the way you've been planning. I really had to let go of all my expectations. When Emma was born, I swore that formula would never touch her little tummy and that she would be breast-fed for the full first year. But since I went back to work, it's been really hard to keep up with my stored supply... so she's had to have formula.
Anyway, all of that just to say, that formula is fine. It's not the horrible evil I thought it was! :) Emma usually takes between 5-7 ounces at a feeding (she's 3 months old), but that's about how much breastmilk she takes from a bottle too. I will say that we decided to give Emma formula for her last feeding, and it has helped her sleep longer through the night. We use Enfamil with Iron and Enfamil Gentlease. Its what the hospital and our pediatrician reccommended. One suggestion is to ask your doctor for some samples. They get tons and tons of cans of formula as free samples. My pediatrician said that we can get it from them whenever we need it, so we've never had to pay for formula, and as long as we keep asking for it, we never will. I would think it'd be worth a try to ask your doctor.
I would just encourage you to not beat yourself up over your situation. I know its hard. Its really precious to share nursing with your baby. But you can still have that time. Maybe you can just spread out your nursing sessions. Because I teach school, I nurse first thing in the morning, when I get home from school around 4:00 and then usually once, maybe more in the evening before she goes to bed. Also, even if my breasts are empty and seem dry, if I pump for at least 10 minutes, I seem to have more milk the next time I need it.
I know this response was really long. I'm sorry, I guess I just really related to what you're going through. I hope I was able to help a little... even just to be encouraging.
Good Luck! And remember, the fact that you've nursed this long is so great for your baby. :)
-S. & Baby Emma