Massive for you - it is awful!
The biggest thing I have struggled with is the 'helpful' suggestions as to why my DD1 is/was a non sleeper.
To be honest (and I certainly hope this is not your experience) she doesn't often sleep through the night very often and she will be 4 in June. We have tried pretty much all options (mostly under duress and out of sheer desperation so perhaps that is why they didn't work??).
To try and maximise everyone's sleep (mine especially) she has started coming in with us (about 1 year ago) when she wakes. I wish I had put my foot down earlier (with Dh as he was anti cosleeping) as rather than an all night party she snuggles in and we all go straight back to sleep. So not perfect but much better.
Also I am convinced it is her - DD2 is a great sleeper despite her big sisters lead - so please do not waste the little energy you have blaming yourself.
Good luck! xx