Sorry to hear about Mushroom,
We have exactly the same problems with our boy Jess, he is a very stressy cat, so we know its stress related, we have 3 feliways plugged in. we rehomed a kitten in Jan and it was also suggested to us that his hasn't helped but they get on fine and Jess was suffering before Milo arrived.
Do take mushroom to the vets especally if there is blood, try cutting out biscuits (we've done this with Jess) and adding a tablespoon of water to the wet food.
Its very hard to deal with and you need an understanding vet,