It really does get better. I am so sorry to hear you are feeling like this and can totally sympathise, i think many women experience this, though what can make it harder sometimes is the impression that everyone else is taking everything in their stride, its usually not the case, you just see the good bits that's all.
My DD has colic for first 16 weeks, everyone told me would get better by 12 weeks, it was awful, i felt like i was counting down the weeks, just wiling for things to get better, the magic 12 week mark came and it didn't stop, i thought it would never end. My DD was also difficult to settle outside of colic and would nap for long at all. I remember meeting a colleague for lunch, DD wouldn't settle, cried a lot, i didn't eat my lunch but walked around the restaurant, embarrassed, thinking people would be wondering why i couldn't calm my baby, im sure no one noticed but experiences like that do knock the confidence out of you.
I promise you it does get better and you are doing a great job. It took me a long time to realise that my baby's cry sounded soooo distressing to me but to others it was just a little baby crying a bit.
I have to admit, before, I had DD i never considered that i wouldn't be able to console her, i thought it might take me a while to work out what she liked best, but i always thought this was a mum's 'job' and when i couldn't do it i felt a massive failure.
sorry, its a bit long but you are not alone, and it does get better, honest! I bet you are doing a great job!