Mommy's boy

My 19m old boy is a mommy's boy. When he wakes up and slept poorly he cries for mommy, when he needs his diaper changed, he cries for mommy. When he wants to play it is mommy he needs to play with him etc. But mommy is 32w pregnant and tired, can no longer pick him up and loses her patience after a while. I love that he loves me so much but I am scared that when number two is here and he will need to share me, he will go bezerk. Plus my entire body is just overtired and cannot take much more. Please tell me this is a phase? Anyone have any tips? We try to not give in and let daddy change him, I tell him off when he is being naughty (so mommy isnt always the good one) and I dont pick him up anymore. But it doesnt seem to suffice. I really need some tips to handle this! Anyone?