Help, I'm so confused! Worm problem??

This is about my four year old cat, Adrien. Since August I have taken him to the vet three times for various reasons. At first I thought it was his pica. He has a tendency to chew plastic, and at times I've found it in his stool. So I hid all plastic. Then in September he got really lethargic and hot. I found him hiding under my bed. I took him to the vet and they were very unsure. They gave him a shot, I think it was for worms. They wanted to do blood tests but I didn't have the money. I was going to come back a week later for that, but ... my other cat got worms. The little rice stuff stuck to her bum. I didn't have the money to go back after that, as I don't have a car and have to take a cab either way ($30). They were both put on Revolution but my other cat was given some extra pills for worms at the vet, I think. She hasn't had problems since. Now my first cat, Adrien, has rice stuff stuck to his bum (I'm really sorry about the image): 


I thought the Revolution would prevent this from happening ... I'm really starting to worry that this could be a lot worse. I don't know a lot about worms, but I'm worried that because of his previous problems that I thought had to have been caused by his pica ... I'm worried it might be heartworm. Does heartworm have the rice stuff symptom?? I'm so scared and I don't know anything about this stuff. I'm going to take him to the vet on Monday for blood tests and whatever else they need to figure this thing out, but I wanted someone's opinion right now about this. After his last dose of Revolution (the day after) I found his bum COVERED in this stuff. I gave him a bath and it was fine until now. My mother told me it was normal, but I don't think it is now. Oh I'm so frustrated. 

Help!

With deworming your cat will need to be treated three consecutive times. It is normal to see more worms in the stool later treatment, but the treatment only kills the adult worms. You continue treating in two or three week increments (whatever your vet advises) to kill the worms at all stages of the life cycle.

That looks like tapeworm segments.  You need a special wormer for them.  Revolution won't kill tapeworms.  Also, be sure you're treating for fleas since tapeworms come from ingesting fleas.

In my organisation upon intake of new cats we treat with Revolution, then  Pyrantel after two and four weeks. That usually takes care of roundworms. Tapeworms need Praziquantel You can get Praziquantel over the counter in pet stores, it´s tablets or capsules. Pyrantel is liquid. You can buy liquid dewormer in the pet stores too, although I don´t remember the product name.