OP I feel for you, I had the same with mine and its so so hard.
There are many reasons why a baby can't sleep through. Some have easy solutions, some have difficulty solutions and others don't have any. The problem I had was that online you have a million "experts" telling you what you should be doing. And I would try one and worry if I should be trying one of the twenty other solutions I read about.
A sleep coach helped for me, not because she helped get DS to sleep but because I felt we had a plan we work on together and tried things with a clear goal. And I didn't feel I must be doing something wrong because I had someone telling me I was trying all the right things.
My child never slept through, woke up at between 8 and 16 times a night until at least 15 months. Not saying this will happen to you, most people try things and eventually find something that works. But just so you know it's not something you are doing wrong. Some babies just can't connect sleep cycles, it's something they have to learn on their own. Just like rolling over, walking and talking, some learn it fast than others but they all get there eventually.
For me things started to get better at around 15 months and from 2 and a half he wakes up around once a night. Even now at 4 he wakes at least once and I go and sleep with him.
I know a few people who say that a osteopath really helped their child sleep better. Maybe worth a try, I went at around 4 months but it made no difference to us.
The thing that I wished I had done sooner is buy a single mattress and co sleep with the mattress in the floor. This made the world of different to my sleep.