Cat Rubbing Bottom

I have a one and a half year old male cat. Lately he has been dragging his bottom across the floor after he uses the litter box. I have also recently changed his food. Could this be the reason for his new behaviour? If not, what else could be causing him to do this?
I would appreciate any help.

Cats do this sometimes if the have worms,I think. Has your kitty been dewormed lately?

I have never had him dewormed...what causes this? Is it the food change? What can I do to prevent this from happening (if it is indeed worms)
Where do I go to get this done? In the past I have given my cat's pills...is a vet trip necessary?
Thanks for the help!

When a cat drags their but on the floor it usually means one of two things: they could have worms or they feel like something is still on their but after they use litter box. My cat patches does this but it is because she feels something (it's not worms). Cat's don't get worms from changing their food. Is you cat outdoors and does he have fleas?

If he does it on a regular basis, I would ask the vet to check a stool sample. It is better to treat when needed and not just because if the cat is indoors all the time.
Yes, he could be eating things that are stringy or maybe even a little hairball is passing which gives them and itch.
The last thing is the anal glands. Most cats can express them when they go to the bathroom. Sometimes it is not enough and they will scoot to help express them.