A lot of TwentiethCenturyHeffa's first post I could have written.
My DS didn't BF. He just wouldn't latch on. I expressed for several weeks, and could express for England but... I was on my knees with tiredness, then I got mastitis twice (delirium level temperatures within 4 hours). We gave up and switched to formula. At that point DS got a lot happier and his nappy rash disappeared. And I felt so terribly bad about failing to feed. In tears when I thought about it bad. 
Between pregnancies I read a single blog post from someone who had had problems with their daughter, and then had been fine with their son. It gave me hope.
Pregnant with DD, I read the breastfeeding posts on this forum and felt awful and guilty and all sorts of negative emotions about my failure over my son's feeding. I would sometimes cry and avoid these pages, but kept coming back. I felt horribly defensive against those who bashed formula feeding and hated the way the breast is best message had made me feel. But, I realised that I hadn't had good support.
I eventually got up the courage to phone the local breastfeeding counsellor at around 36 weeks pregnant... I was in tears and unable to speak within 2 minutes of her answering the phone. But we met, and we had a plan laid out. I had (controlled) gestational diabetes with DD, and we planned to express colostrum so we could feed it to her if she had a sugar crash and went dozy. That gave me a mental buffer too, so she'd get something good even if everything went pear shaped. Hours and hours of hand expressing drops of the liquid gold...
Roll on the birth; instead of spending 51 hours in labour with me getting tireder and tireder, she came in a couple of hours. Instead of needing some time in the care of a paediatrician we could have skin to skin immediately. She latched in the delivery suite, knew what she was doing. I have a photo of her with her tongue stuck out at an hour old - DS didn't stick his out till 3 months (oh, yes, I did ask about tongue tie but was told there wasn't one). She didn't go dozy. The first thawed batch of colostrum, which took about 30 hours to produce, went down the drain because it had been thawed and unused. (Oh I felt awful and wonderful at the same time doing that). I had some problems with latch and resorted to a bottle (when we popped in the rest of the thawed colostrum) and nipple shields in the first two weeks but at 11 weeks we're still breast feeding and I am thrilled.
In hindsight:
I probably had gestational diabetes (GD) with my first pregnancy, but it wasn't looked for. We think my son had the resultant sugar crash, he didn't seek food and was dozy (as well as having a cardiac problem common in uncontrolled GD babies). He was also put on antibiotics as I was found to be carrying group B strep (GBS) (I should have been on antibiotics in labour due to the prolonged rupture of membranes, which would have meant he didn't need them). The antibiotics probably made him dozier. Inexperienced at picking up babies, and exhausted, I couldn't get him out of the hospital bassinet safely (too high). We were in hospital for 5 days due to the GBS. All this meant too little skin to skin and bonding. We had mixed messages and poor breastfeeding support from too many different people. "It should hurt" and "It shouldn't hurt". Having now experienced correct latch, I think my son may have latched once or twice in hospital but having been told it shouldn't hurt we unlatched him and I think that contributed to the failure.
With DD, initial latch hurt but not the main feed. Now not even initial latch hurts, unless she comes off and puts herself back on too quickly for me to stop her onto aureola and not nipple. Nipple cream, shields and shells, determination, knowing about cluster feeding, getting help with positions, daring to ask the BF counsellor to come and visit, having a BF counsellor I trusted from before the birth, having hope and knowing it isn't the end of the world if we failed again.
And it's been amazingly cathartic to write all that. 
And having formula fed one and breast fed the other... I found formula easier than the bits when I was struggling with breast feeding... breast feeding is easier in the middle of the night and out and about at the moment, but I can't just hand my baby over to my husband and say "your turn for a bit" when she's fussing horribly. I still think the "breast is best" message and the huge guilt downer on formula feeding mothers is over the top and could contribute to a lot of baby blues problems. I still feel bad about DS, but not as much of a failure just because I have succeeded now.