No, you are NOT expecting too much.
He's 4, and you are pregnant... maybe it is making him feel awkward.
Regardless, he has to help.
Be consistent.
Don't debate about it. Don't reward him. Don't bribe him.
I would, tell him that you need help... you are pregnant and you cannot do everything... and to help Mommy... as a "team" emphasize TEAM WORK... my son is 3.5, and he LOVES when I say "Team work".... or I just tell him point blank... he is a PART of a family and family helps each other. We are a TEAM. Or that I am busy/tired and we ALL try to help each other. And my kids do help. They put away.
I would not offer him 'rewards' for 'helping. Helping is helping. That is what family members do.
If he does not help, maybe tell him to pick up 4 things. With you. Maybe the idea of picking up EVERYTHING is overwhelming for him.
Or if he does not help at all... gather it up... and put it away in a closet. A toy time-out. Don't say anything, just do it. Then, he is smart enough to realize what is going on... just put his toys away where he cannot get it. He then has to realize or earn it back. Or put it in your room.
The thing is, you are also pregnant. When I was pregnant with my 2nd child, I explained in simple terms to my eldest, that Mommy being pregnant means I cannot do certain things like before/ that I need to rest/That I cannot bend over real easily/that I need 'help'/that I can't lift heavy things etc. But I made it in a comforting way... not 'demanding' it from her... I approached it in a 'team' type way... and that I am proud of her... for being thoughtful.... My eldest was about 3.5 when I was preggers with my 2nd child, and she was REALLY great about it all...
Or maybe your son is trying to get attention because you are pregnant... which is normal too. A young child can't always cope... nor adjust to it all.
Maybe he needs more one on one time...and just sit down with him and talk with him.... not judging/lecturing, but making him feel assured and peaceful about it....
A child this age CAN help and do chores. My son who is 3.5, can even scramble/cook his own eggs.While I supervise. He will even put his leftovers in the fridge, he will even put his dishes in the sink and get his own drink etc. You just have to teach them. And don't expect TOO much... so instead of cleaning up the WHOLE room... make it into smaller expectations... like have him pick up 4-5 objects and put it in a basket. Put in a timer. Put on a song... and when it stops, that is the end time.
Try making it more attainable...
just some quick ideas,
all the best,
Susan