Not so good poo.

I have a two year old cream domestic, I adopted him from a shelter at about 9 months. Took him to the vet and was given the all clear. Well the first week we had him he was on the front porch (enclosed) and he went on a pile of newspapers. This is when I first noticed blood in his fecal matter. I called my vet and she said its most likely nothing but food allergy, try this and if it doesn't clear up bring in a stool sample. Well tried that food not much better. So I tried a higher end brand of which I did research on first because what the vet had me try was Purina sensitive systems. What I found was a grain free. It worked, no blood in his fecal matter. Well, I was cleaning the litter box on the front porch, its his favorite to go in. And since it wasn't there he pooped on a flattened box I use to put shoes on. And there is yet again blood. Just wondering if anyone has had these issues, or knows of what it could be. I go to the vet tomorrow for my dog who needs a shot and will be seeking a course of action to take. But my cat is a very active and seemingly happy ball of fur.
Although I am fully committed to my furry loved ones, I am currently battling a possible liver disorder in one cat and can't seem to find much information on cats bowel diseases or issues to get an idea of what the possibilities could be.

Anything at all would be so greatly appreciated!!

here's a link that could possibly help you determine if it's a serious problem or nothing to worry about depending on how often it occurs and what shade of red the  blood is.  http://www.cat-world.com.au/Cat-Health-Collection/blood-in-cat-stool.html

A small amount of bright red blood on the stool is often a sign of constipation.  Is it very small amounts in random places rather than in the litter box?  There are some things that can be done to prevent constipation, first being an all wet diet to increase the amount of water in his diet.

Another of our member @IrinaSaK has had a cat with blood in her stool on and off for awhile, although I believe she has finally resolved the problem (I think) with the right foods.  She is in Europe though, so depending on where you are, those foods may not be available.  I have marked this message so she will see it and hopefully respond.

Thanks for the link and your comments. I spoke with the vet today whilst there getting a depo shot for one of my dogs and they want a stool sample and said we may have to put him on a prescription diet. I will probably look into wet food or see if they recommend wet food for him also. I have also looked into adding pro-biotics, but I guess we shall see what the stool sample reveals. And it is a rather bright red, mucus with light brown fecal matter.

He has never gone outside of the litter box unless he was somewhere he couldn't get to one. Like the front porch when I was cleaning the one that goes there or when my boyfriend accidentally left him in the bed room. I know for sure he has had a bloody stool when he has some dried blood on his rump.

I hope she responds as well and thank you for tagging her.

Much appreciated!!