I know this is a very rare thing, but I have an issue with hormones in every which way which means I don't respond in the normal way for pretty much anything.
Breastfeeding was a case in point. With DS, I managed for about 8 weeks, but during that time I bled constantly. The weirder reaction was something with a 3 letter acronym that I've forgotten. The symptom of this is that on let-down, it causes urges of violence towards your baby. I had no clue what it was about, but was obviously distressed at the images of swinging my baby by his legs against the radiator or biting a chunk out of his cheek.
Towards the end, I exclusively expressed which helped, because I could do it when he was asleep or was safely in his chair, and the actual process of feeding started to feel quite a lot nicer. However, having to sterilise and reheat gave me the hassle of bottle-feeding and the exhaustion of breastfeeding.
With DD, I developed the same symptoms quickly, but I was aware of what was coming so switched to expressing while the baby was not on me straight away. I managed about 6 weeks.
I have no idea if the children would have been healthier or happier or better sleepers on breast. Either way, it was the safest option for all concerned.
The best thing that anyone said to me was a friend who was a breast-feeding consultant. 'I know what that is, it's not your fault, and if you need to switch to formula, don't spend the rest of your life tearing yourself apart because you've done so.'
If I had baby 3, I would have done the same again, though started with the expressing much earlier - within days. It didn't happen though.