My cat is being strange

[Rattysparklebum]

I adopted a sibling pair of female cats nearly 3 years ago when’s they were around a year old, they have free access to a large garden through the cat flap, they play chase together all the time and sometimes sleep together still.

One of the cats has recently started peeing on the door mat so we reintroduced a litter tray, said cat now goes outside, comes back in to use litter tray then goes straight back out!

Both cats claimed a cardboard box last week from an amazon delivery and took turns sleeping in it so I got another box so they could have each and not have to share, said cat has now gone an peed in the new box!

What is going on and how do I fix her?

She might be suffering from cystitis if she's urinating in a cardboard box and a doormat. Vet visit is in order if this continues or you notice her going more frequently, straining, only urinating small amounts at a time, any sign of blood in her urine, or general signs she is unwell (not eating/hiding etc.).

In general though, all cats should have litter trays always available. The gold standard is a tray per cat + 1 extra, in quiet places around the home. Can you imagine having to go to the loo in the garden in this weather, potentially with a neighbour's cat around?