Blood in my kittens stool

I have a kitten who is approx. 13- 14 weeks old. I have had her for a few weeks now and she has been dewormed twice. Did this as a precaution when i first got her just in case she had them. I never noticed blood in her stool until the other day. Which we had changed her cat food a few days before that. I am wondering if the food we had her on caused her intestines or something to cause it to get irritated. We switched her back to her original kitten food now to see if that helps if not i will have to take her to the vet. Anyone have any ideas what it could be besides worms???? Let me know please

Is the blood mixed in with the stool or does it seem like it's on top of it? Is it fresh/bright? Any slime?
If it's on top of the stool, bright, and there's not more than perhaps a spoonful, it's propably caused by irritated rectum (or was it colon, not sure) which can be caused by food, stress, new bacteria (for example in new home) etc. Usually easily treated but if it doesn't get better I suggest testing for giardia.
If the blood is dark or mixed in with the stool, it's more likely something more complicated and needs vet asap.
I don't have any advice about the worms though (I've never had to deal with them).