My cat has stomach problems Can one give me a clue what to do?

Our 9 yr old  name is Zipper and is a  solid black long hair Himalaya has problems with accidental  droppings of poop. It is very dark almost black. He eats a dry food with limited ingredients that the vet prescribed for him. during the day.  We also were told to use Fortiflora (1 package daily). We mix it with about 4 oz at night of natural balance duck & pea. He has done very well on it for about a yr and now it does not seem to be working. He acts like he has no energy, sleeps a lot and his coat looks wild and wooly.

Any help with this? Zipper will appreciate your help.

I'm not sure what you mean by "accidental droppings of poop." Do you mean that he is getting diarrhea? Or pooping outside his box? Or is poop just getting stuck to his long fur? 

If it's either of the first two, unfortunately another visit to the vet is in order. Anytime cats have significant changes with their bathroom habits (including a change in the color/consistency of the stool or where they are depositing it) you want to get it checked out and make sure something more serious isn't going on. It's possible that he has picked up a parasite/infection, has developed a food allergy, or has something like IBS (irritable bowel syndrome). And, unfortunately the only way to narrow down the cause is by a physical exam and examination of the stool. 

So, make an appointment with your vet ASAP. They will likely want a stool sample as "fresh" as you can get it. So, monitor the box and try to get the sample before it gets buried in litter. And, you can keep it in the fridge for up to 12 hours if necessary. 

After you meet with the vet come back and let us know what they said. We have a lot of users that are very familiar with each of these issues (and many I didn't mention) and can help you make whatever adjustments are necessary. And, please don't hesitate to ask follow up questions, especially if I am misunderstanding the situation. 

Vibes for both you and Zipper. Welcome to TCS!!!! 

Is the stool tarry in texture? If so, being "almost black" if tarry most likely means there is blood from upper GI bleeding. A vet visit is definitely in order.