Stressed, unhappy and never off the litter tray... what's going on?

Dear George,  
I am a very troubled boy, and I hope that you can help me.

 I lived in a nice house with my human, and I liked it very much. I had all my things around me, direct access to the garden and I was very comfortable and relaxed there. It was my house – my home!

 Then about 8 weeks ago, there was lots of disruptions all my things were packed away and I was put in my cat basket and taken to another house – a strange house, with lots of strange smells…and none of them my comforting home smells. Obviously I was distressed by this and began meowing continuously to my human and pacing up and down the rooms. My human tried to comfort me by stroking me and talking softly to me. She also put down worn items of her clothing in different rooms so I could smell her everywhere around the house, but it still didn’t calm me.

 As the weeks went on my agitation grew and I just couldn’t settle. My agitation was made worse by the fact that we are now living in a flat, so I have to go out of my house and down a strange ‘shared’ corridor to get outside. And there is another cat who lives next door to us that uses the corridor too, and he didn’t take kindly to me using it and spat at me. Now I am even more upset. My human bought some Feliway plug ins, and whilst they calm me down for a while, my anxiety comes back.

 I have taken to using my litter tray constantly, sometimes as much as every ten minutes, which has given me a very sore and irritated bottom and I sometimes have a bit of blood in my urine. My human is very, very worried about me and doesn’t know where to turn.

 A few months before the move, I got lost for a number of weeks before I was found and re-united with my human. I was a rather traumatised from the experience, but soon settled down back in my home. So I don’t know if this has anything to do with my reaction now at the house move?

 Can you help me George and help my human to understand why I’m behaving like this and not settling down?

 Yours tearfully,

 Thomas.

Dear Thomas,
There is few things more upsetting to a cat than moving house. There you are settled and happy in your territory, when suddenly your pet human stuffs you in a cat box and turns you out into a strange new place. All the smells are wrong. You don't know where anything is. And it feels very very unsafe.
Most of us hide under the bed for a day or two. But some sensitive cats like you suffer from stress-induced illness. All that going to the litter tray is, I fear, a sign of cystitis. Vets (loathsome people) call it FIC, Feline Idiopathic Cystitis.  "Idiopathic" just means "we don't know the cause." But we cats do know the cause. It's stress due to house moving.
The earlier trauma of getting lost will not have helped. That must have been unsettling and probably also very frightening. Then this... poor Thomas. Even loathsome vets know that moving house is stressful for cats and can result in FIC.
Having to share the corridor with another strange cat (who hisses because he is frightened too) is another stress. Perhaps your humans could invest in a cat ladder letting you go outside from the window. Or put several cardboard boxes with entrances in them, where you can hide if the strange cat passes by. Or just keep you safely in the flat till you have recovered. My human's website has some suggestions for how to make indoor life more interesting for you.
Why humans insist on changing their territory is beyond my imagination.  They are a very insensitive species. Your letter makes me feel angry about their ridiculous behaviour.
They must reduce your stress and read the instructions at  http://www.catexpert.co.uk/cats/reasons-why-your-cat-feels-stressed-and-unhappy-and-what-to-do-about-them/
Yours with sympathy,
George.
PS. We hate vets but this is one time when you need their help.