Loose Bowels Battle

My cat is going through the exact same thing!! I've had my baby for about 10 yrs and he has always had loose stools with some blood in it. But recently it has gotten significantly worse. For about the past month my baby's stool has been like water, some blood in it, horrible smell and sometimes mucus mixed in. He has been running to the box up to 5 times a day and sometime had accidents. He cries when he has to poop and he'll cry if you pet/pat his back end. He is also very gassy and you can hear his little tummy making noise. I have had numerous blood tests done, FIV, leukemia, worms, parasites, values ... negative on all. I've switched his food to Science Diet I/D hard food and the soft food (which he likes, thank God) with some luck. I've also bought one of those stress-relief plug-ins. I started giving him Pro-Pectalin which is an anit-diarrheal gel made for cats & dogs. I bought it on PetRx.com I believe this gel has helped him alot. I know it's not getting to the root of the problem but my baby was wasting away and no one can figure out why. He was a normal healthy cat of 11lbs and he is down to 7lbs (he's a Turkish Angora and should be heavy than 7lbs). He's not a fan of taking the med but I smear a little on his arm and he licks it off. I am also going to try some metamucil. I heard that will firm up his stool. After 3 days with the Pro-Pectalin his stool went from a water consistency to a pudding consistency with some firmer pieces. I will eventually have to do an intestinal biopsy but my main concern right now is to stop the diarrhea.