I've posted here about this before... My three year old neutered female cat goes through phases of pissing and shitting in our bedroom (particularly on the bed). She has been to the vet countless times. He has said it is a urine infection, has given her an antibiotic injection, and the peeing and pooping has stopped. He has also put her on a urinary diet, which seems to have helped (although she is not particularly keen on it, she will eat it).
The vet also recommended Feliway, as the cat seemed a bit stressed. Her reaction to the Feliway diffuser was to poo in front of it, until we removed it, and then she went back to using her box.
Today she has shat on the hall floor, the bedroom floor and has pissed copiously and lavishly over our bed, soaking two pillows, a duvet, the sheet, mattress cover and the mattress. I am going to take her back to the vet tomorrow to see what he suggests.
She is an indoor cat (and always has been), and lives with our other male cat, who is 5. We took her from someone as a kitten, as otherwise they were going to send her to a rescue place. The two cats get on quite well (they are curled up together now). I suspect she would like to go out (not possible as we live on a main road, in a flat), but she seems quite content most of the time, being in the flat (it's a large flat) with her toys and cat trees. The cats have three litter trays - one they ignore, one they will use if they have to, and one which they both choose to use. Two are in one bathroom, and one in another, which is rarely used.
Any suggestions/anything I can suggest to the vet? DH has "had enough of living in piss and shit" and wants to rehome her. I don't. She is a sweet cat, very gentle, and DD2's "special cat." DD2 would be devastated if she went, as would I. I don't know what else to do. We have been on the cycle of antibiotics, special diet, then three or four months later, the peeing and pooing starts again, back to vet, more antibiotics, repeat ad infinitum. Other cat is clean and seems happy.