Before he was born, everything was fine. Universally, children just seem to interfere with sex. It has to do with the change in their body, their role, etc. It may take awhile before their enthusiasm returns. It actually might have to do with hormones as well.
Men fall asleep because it is so relaxing.
Many people use sex as a sedative. They lie there in the afterglow and fall asleep. If you always have sex at night and it is the last thing you do, then you will condition yourself to fall asleep. Try doing it earlier in the day. That has to be the last question for this chat.