This is going to sound quite corny but I think that both partners being able to communicate their needs/feelings is really the key to being happy in a relationship. Being disgruntled with your sex life as a couple is a symptom of this. With everything there needs to be give and take but that is so much easier in theory. This can be really hard to maintain when you are exhausted, recovering physically (and often mentally from birth) and are finding your way as a mum (and Dad for that matter). Certainly from my perspective it can be all consuming and it is really easy to assume that everyone is on the same page or even feeling so underappreciated/out of control that you barely even care.