I notice that my 12 week old kitten cries when she goes to the potty. I have checked the litter box for any signs of worm like things but do not notice any. Occasionally there will be a tiny little bit of blood (mucusy) but very little. She eats great and is very active. Might this be because the vet did a temperature (rectal) on her?
Sounds like she might and a urinary tract infection. You should really take her back to the vet or at least call them and ask them. If she had worms, round worms are more common in kittens. There would be small white and coming out her anus, she'd also have a pot belly. If that's the case, then you need to get her to the vet, change the litter box frequently and follow the vets course of action.