My DS is about 33lbs. My OB has never given me a weight lifting restriction (that I am aware of), so if I need to, I pick him up, but I don't carry him for any length of time, or walk around. The most I'll do for him on a rare occasion now is bring him up the stairs. Otherwise, it's usually to pick him up and put him on the counter so I can brush his teeth, or just to give him a hug. If he wants to stay up longer, then I sit down on the couch and we snuggle that way.
He rarely asks me to lift him, so when he does, I do it if I can, because he has been regressing a bit, so I'm going to play into it during this phase, as he has enough changes going on in his little life right now.