Cat stops cleaning her behind

Hello everyone, I've been a long time reader of this forum but I never posted anything.

A year ago I fostered a kitten and the mother cat who were rescues at the Montreal SPCA, I haven't had any problems with either cats, they love to play, and they seem to be in good health. Although the younger cat, who is about a year old, has stopped cleaning her behind and now rubs her butt across the carpets in our house. I've read that this could be related to worms, but I've checked her litter box and there seems to be no evidence of worms. When she was younger this wasn't a problem, she would always clean her behind.

I suspect the problem arose a couple of months ago, she had a lot of fur and it seemed like she had trouble reaching her butt because of all the fur she had, so I shaved her, she now has the "lion cut" style, but she doesn't clean her butt anymore. I took her to the vet, they shaved the area and the vet showed us she had a couple of bruises from rubbing her butt on the carpet, they had us put a collar on her and rub cream on the affected areas for a week. The bruises healed and everything seems fine, but she continues to rub her butt across the carpet, I'm certain that it's no longer a problem of her being able to reach. I'm concerned that she might bruise herself again and the area could become infected. It would also be nice to come home and not find streaks on our carpets. If anyone on this forum has experience with this problem I would greatly appreciate some help.

It could be anal glands, and you don't necessarily see signs of worms.  Rubbing cream won't help either condition.  Her glands can be expressed - let the vet do this - and Drontal will fix any worms.

I should have mentioned that the vet expressed her anal glands and said that there did not seem to be anything out of the ordinary. I will take her to the vet soon and ask about Drontal, thanks for the help!
 

Although now that you mention worms, it makes me wonder. My cat isn't really the smartest cat you'll ever meet, she tends to try and eat anything that she can fit in her mouth, so its more than likely she might have ate something that was infected in our backyard. I'll take her to the vet ASAP.

You can probably get Drontal without going to the vets.  If you can get Milbemax it's far smaller and easier to five.  In either case you need to know what the cat weighs so you can give the right dose.

Have mother and daughter ever been wormed?  And has daughter put on too much weight to reach her behind?

I live in Canada, would you know where I might be able to get my hands on either of the two?
They have both been wormed, and no the daughter is at a good weight and is capable of reaching.