Cat keeps vomiting and now pooping on furniture

Our 5 yr old calico female cat has always been one to vomit multiple times a week. We put it down to the cat food she was eating so we have changed her diet to just boiled chicken and a digestive support dry food at the recommendation of our vet. However she still continues to vomit frequently. Also, in the past she has always used her litter box to poop but the past 3 or 4 months will occasionally do it on our lounge which is covered in a blanket. Her litter box is clean so we can't understand why. She used to get a bit of blood in her stool and mucus. She did it again today and I noticed no blood but a bit of mucus. We have taken her to the vet for this a couple of times. She was on antibiotics a couple of months ago but the problem keeps happening. We have another cat (male Burmese/Russian blue mix). They tolerate eachother most of the time but occasionally fight. Is this stress related if the vets haven't been able to find a reason? Is it worth trying out the feliway spray that is meant to calm them? I know it works for some cats but not all. I am at a loss. Sometimes I feel like she is just doing it on purpose!

Hello - I'm sorry to hear that your cat is ill and I'm afraid that this is a surprisingly common question. What you have is a symptom - vomitting.  There is no one cure for vomiting, especially not antibiotics (unless the vomitting is caused by a specific bacterial disease which is relatively uncommon).   However, there are many different causes of vomiting.  Your vet could work by trial and error, giving the treatment for different causes of chronic vomiting until they chance on the correct one.  However, this would take a lot of money, false hope and time.  So what most vets will do is to propose tests in order to pinpoint the correct reason.  A really common cause is pancreatitis.  A lipase test does not rule pancreatitis in or out - but there are other ways of testing, so this could be something to ask about.  Ultrasound can identify various other problems.  However, from the description you are giving it does sound as if you also have a stressed cat, who is avoiding their usually preferred toileting sites.   How long have you had the second cat / since he came of age / something else shifted in their relationship?  Even cats that dont get on dont always fight; they don't have highly developed evasive body language like dogs do, so sometimes they just co-ixist under stress.  Stress may predispose to other underlying diseases eg pancreatitis.   So, Im afraid that the answer to your problem is, that tests are needed and furthermore, whether it is involved in the vomiting or not, keeping two cats together that don't get on can be very stressful for them and it may be worth considering keeping them apart / in different household to see if it makes any difference to the cats' behaviour in general.  Your vet, however, ought to give advice more appropriate to your particular cats, as I don't know them.  It is likely for example that there was a reason behind those antibiotics.