Have you carried out this action and took it from her hands for a weekend so she can chill with friends or go spa?
And I mean not once but at least a few times ? If not these are just empty promises on your part.
If you have done this and continue to do so then you need to explore whether she is going through some post pregnancy depression as @Saredo mentioned, they are pretty common.
I am surprised none of the females on here have chipped in on how to identify this and how to best treat it @Gambar @Saredo @NotMyL
You need to exhaust all avenues first, rule out the above and do your part, if that no longer works seek family mediation as per sunnah, you appoint someone, she appoints someone and let them both talk and make a ruling as per sunnah.
By the way, do you regularly make the dua regarding your wife and children becoming the coolness of your eye ? If not you need to incorporate this after every salah.
It’s simple, was she nagging you about everything before the baby? Having a baby changes some women more so than others, if the “nagging” is new thing then you know it has something to do with the baby.