My 2.5 yr old female, Babs, is having issues with constipation. She threw up some clear, slightly mucusy liquid (gastric acid?) on Wednesday and hasn't been quite herself since. On Saturday we noticed she hadn't pooped since she threw up so we took her to the vet. They ran a radiograph which revealed a significant amount of backed up poo (though no other issues) so they gave her an enema, cleared a lot of poo and sent her on the way with some lactulose.
Since then her eating and drinking have been completely normal but she still has not pooped.
Originally my thinking was that the constipation was the result of a dietary change and stress. She stayed with a friend of ours for a week over New Year's. That friend has 2 other female cats and Babs had unfettered access to their dry food, which she probably pigged out on. The vomiting incident was 2 or 3 days after her stay there.
Now that she still seems to be constipated, I'm wondering about other potential causes. We took in a stray now 3-month-old kitten, Frank, a month ago. We only started letting him out of his room at the beginning of last week, as he was dealing with a coccidia infection and a leaky bum. This means that him having access to the house (and theoretically Babs' litterbox) coincides with the beginning of her constipation. Thinking on it this morning, I think she is peeing less even though her fluid intake is completely normal.
My question then is: is it possible that she now doesn't want to use the litterbox because he has access to it? I read somewhere that cats can feel cornered in a covered litterbox, which hers is. Even if that is the case, would she hold her poop in to the point of being constipated or would she simply defecate elsewhere in the house?
Babs and Frank are friends and they play for hours, but I know that cats can be neurotic.