Kitten, diarrhea out of nowhere

My 14 week kitten has never had any problems using his litter and his stools have always been normal. However, last night his stool was quite soft (not completely diarrhea) and glue like and it most of it got stuck to his tail and fur. We had to completely give him a bath. My kitty has been eating normally for the past month (we got him a month ago). He has been eating Nature's Variety Instinct, Nature's Variety Raw and Almo. Most recently, we started adding Weruva Truluxe to his rotation, he's only eaten it once and that was on Monday. He had the loose/soft stool on Wednesday night. Can anyone tell me if that could be related as I know a change in diet can cause an upset tummy. However, that was 2 nights ago. He was also de-wormed the weekend before we got him.Can anybody give me any ideas on what could have caused the soft stool? 

We are also going to the vet this Saturday for a general checkup. Would it be worth it to bring a stool sample in? 

Thanks!

My initial thought is that he may need to be dewormed again. It's normal to do more than one round and these are typically 3-4 weeks apart to make sure you cover the life cycle of whatever parasite there is (typically roundworms and tapeworms in kittens.)

If he only has/had the one episode of soft stool and subsequent stools are normal, it would be possible for the soft stool to be linked to the new food. If that is the case, read the ingredient list and see what is different than the other foods (this can be the protein, a gum/thickener, or even the use of egg product.)

If the soft stool persists, than, yes, try to take a *fresh* stool sample with you.

Update: kitty was fine today and his stool was back to normal, so maybe it was just a passing thing. I will take your advice though and bring in a sample for the vet anyways, just in case. Thanks!