I've never posted before but not sure what else to do.

I've been with my partner for 4 years, the first 6 months, sex life was amazing and then out of nowhere it just plummets, he either can't get hard to start with, or he gets soft half way through or he cums really quickly so I literally get nothing from it ever and have to secretly sort myself out when he's not around. I've just kinda got on with it, we've argued a few times about it and he says he will get help or work with me to fix it but then we don't have sex for ages and when we do the same happens again, we actually stopped having sex completely when we had our daughter for about a year and now we've decided to try for baby 2 but everytime I ovulate he can't stay hard or cum so obviously it doesn't work. Anyone else suffers with this? Any advice ?