How long to pump 3 oz?

Michael Jude will be 4 months old on Monday. He's nursing 70% of the time, 30%
Similac thanks to his intensive care stay where he was indoctrinated to
formula. Also he never seems satisfied at the breast and minutes after 30 mins.
of nursing will carry on and then suck formula down like there is no tomorrow.
I have found the whole breastfeeding thing very discouraging sadly enough
especially since I felt so strongly about it and really wanted this so much.

I offer the baby my breast for all his sucking needs and the only time I have
resorted to formula was when he cried uncontrollably after nursings and it was
very obvious he was still hungry. I am now a stay at home mom and while there
is no real need to pump, I have pumped quite a few times so that I can
physically see what my son is getting as he has a bowel movement only every
four days although he does have many wet diapers. I generally get only about 3
oz. in about 45 minutes from both breasts. I am wondering if my breasts are
not producing enough milk. Any time I give him formula, I pump to stimulate my
breasts as I recognize the relationship between supply and demand.

I have heard that women who don't gain a lot of weight during their pregnancies
or whose breasts don't get larger have a tougher time. I only gained 11 pounds
( I was a bit overweight however, and had gestational diabetes so I had to be
very prudent with my pregnancy diet) and my already very large boobs did not
get larger at all. I wore the same bras throughout my pregnancy.

I've read all breastfeeding material I could get my hands on and the sentiment
always seems the same- that all women are capable of breastfeeding, that's it's
what nature intended, and that with practice and perserverance the art can be
mastered.

I, however, am feeling very down suddenly about the whole thing as Michael
always seems hungry and never seems satisfied at the breast. The idea of
supplementing never seemed like a good one, however, his hungry cries get the
better of me every time.

Advice? I don't want to give up. My doctor assures me that if I make it to 6
weeks I'll have done a good thing, but I really wanted to make it to a year if
that was possible.

Thanks for listening,
lisa