Oh mama, you are really not alone in this, so many mums here have gone through the same exhausting stretch and come out the other side just fine. Please do let your gynae or PD know about the fatigue so they can check your iron and make sure both you and baby are getting the right support. In the meantime, try to rest whenever your 4-month-old naps, and do not feel guilty asking your husband or family to take over even for a short while. You are already doing so much, so be kind to yourself during this season.