When does it get easier?!

Our baby is 15 weeks old and I am wondering when does it get easier?! I want a little bit more sleep and I want my shoulder and back, back 😫 (What I mean by that is it feels like they are ready to fall off ) Please tell me everyone goes through a crying baby who only wants to fall asleep in the arms before getting placed in their bassinet or crib?! My lower back is not the same anymore either, I don't know if that's from picking her up or me leaning my body out on the couch to support her as she lays over my shoulder? And does every baby want to be held after they have been burped, changed and fed and just stay awake on you and not want to be put down just to "chill" and "hangout" lol