When is it the right time to have sex again-newborn baby?

My bf and i want to have kids after we get married. We are both in our 20s, live together and have plenty of time to ourselves, majority of that time we spend making love. Once our newborn baby is born, when is it ok to have sex again? I have heard that it can be quite painful at first, is this true? Also, does sex get easier when the baby starts getting older(months old)? I know there won't be as much time as before, but i just don't want to seem like i'd be neglecting our baby. My bf and I aren't like that, we'd give our baby the attention that it deserves and needs.