No practical advice from me (pregnant with my first and planning to BF) but:
8 weeks of this I feel like the worst mum in the world and that I'm failing her and think it would be better for all of us for me to just go back to work.
and
I'm really reluctant cos selfish as it is I WANT to bf and I've worked so hard the past 3 month at it I'm reluctant to give it up. It's also the one thing I feel I actually can do cos I seem to be failing at everything else.
It sounds like you are very stressed and upset. Please make sure you get help from your DH or other family members between feeds. You are not a bad mother just because your baby cries and finds it difficult to settle. You are not being selfish in wanting to breastfeed - it could be the least selfish impulse you have.
Your baby isn't crying because you aren't a good enough mum, her crying is not a judgement on you. Honest. You are doing everything you can to help her. Hold onto that. She wants to be with you. She's just having a tough time with this reflux at the moment.
Sometimes babies cry and we do everything we can to soothe them and they still cry. There is value in someone (you, your DH or a helper - do feel free to take turns) just holding her/being nearby/speaking to her and letting her know that when she is upset or uncomfortable, someone cares enough to be there with her, even if they can't wave a magic wand and make the source of her discomfort go away. Its her first experience of human compassion. What you are doing is worthwhile and enough.
Keep feeding her, keep trying medicines for the reflux, keep trying out different ways of soothing her (in the hope of finding something she likes) from low stimulation like her lying on her slight incline in a darkened room with just a soothing hand, to dancing around the livingroom whilst holding her and singing and some fresh air walks in the pram or sling. Keep doing all the great things you are doing to try and help her. You are enough, honest.
About formula, (I agree with others that it might not solve the problem and make make her symptoms worse if she's intolerant to dairy/soya, and the change in diet may upset her) do remember that if you try it out and she does get some sleep or settled time, then it doesn't mean that you have to make the switch total or permanent. You could just start breastfeeding the next feed in a more relaxed state (when she and you have had a break) and see how that works.
I forget if you've said whether you/your dH have tried feeding her expressed milk? Does she take a bottle? I'd try this option before I'd try formula myself even though I can't stand the idea of faffing around with bottles at all and hope I'll find breastfeeding easy
Please feel free to redirect me to this post in a few months time when my baby is born. I so know it must be difficult to hear your baby cry when you've tried everything.
Take care of yourselves xx This isn't forever, she probably won't cry like this when she's 16.