help!!!

Hi, i got my pup at 8 weeks old, shes had terrible runs and cries to get out every hour so i took her to vets. they prescribed Protexin Prokolin and was told feed her rice and chicken, after 2 days her poops went solid but next day back to water, the breeder had given me pedigree chum pup biscuits and from what ive heard its not ideal, we have tried changing her to Iams puppy food and was told to try natural yogurt, can anyone confirm this and is there anything else i can do, could i be feeding her to much?? how much would be the recommended amount ??, Thanks colin