I chose The Pumpkin Eater for the 1962 Club because the title seemed vaguely familiar (aside from its nursery rhyme connections) and because I don’t think I’ve read any Penelope Mortimer. I think the title is familiar because there was a reasonably popular movie of it in 1964 starring Anne Bancroft.
The unnamed narrator is a wife and mother of a large number of children, the number, names, and ages (except one) never specified. At a young age, she was already married three times, once a widow, and already had quite a few children, including three stepchildren whose father died. As the novel opens, she is recounting a discussion with her father to her psychiatrist, in which her father is trying to dissuade Jake from marrying her, basically saying she is too flaky and has too many children.
As she goes on to tell the story of her marriage, nothing improves. Her psychiatrist thinks her desire to have more children is a pathology (and also entirely her responsibility). Both her psychiatrist and her doctor are disdainful and condescending to her. Nothing seems to be thought of her husband having affairs (although she naïvely believes he is faithful for quite some time despite an early incident with a girl named Philpot).
The fact is, Jake, a screenwriter, is gone on set most of the time, most of their friends are his, the family is wealthy enough to have servants, and even the children are absorbed by nurses early and by schools later. So, she has little to occupy herself with except small children and cooking.
This book is billed as black humor. I didn’t find it funny, but I did sympathize with the narrator. Some horrendous things are done to her, and all of the men around her are manipulative. I thought the novel was bleak rather than funny.
whatmeread 
I read this last year and was really impressed with it, but I agree with you. I didn’t find it funny at all.
It has a pretty seering story.
Oh, dear, I mean searing.