My Kitten has had an extremely loose stool for about 3 weeks, Need some direction.?

We have a kitten that is about 4 months old. Her bowl movements are VERY loose. I have a dog, and a Cat, which the kitten seems to eat both of thier foods as well as hers. Recently I changed my older Cats food to the food the kitten is eating hoping this might help out. Ive also been told this could be something to do with worms? I also wondered if it could be that she was away from her mom at 5 weeks....Is there anything I could be giving her to help her stools. So far the bowl movements are controlled...another thing we are noticing is she is a junk food junky...she crys and crys for human food and junk...We do not give it too her but she acts like a crack head around it....let me know if there is anything I can do to help the loose stool.