Help with food choice

I've been having a hard time finding the right food for my 14 week old pitbull puppy. I initially had her on Blue buffalo wilderness rocky mountain red meat recipe at 9 weeks. 2 weeks later I switched to BBW chicken for puppies because i figured the chicken was better for her than the red meat. I started noticing that her stool had gotten a little softer. I ran out of it on Thanksgiving and was forced to grab a bag of Purina ONE smartblend puppy(chicken) from the local grocery store. Though I knew it wasn't the best food her, it worked out because she liked it and her stool seemed to had gotten firmer. Once that ran out I put her back on the BBW chicken and her stool instantly returned to soft and loose. I contacted the pet supply and was told that the protein content may have been a little too high for her and to return it and try the BB life protection lamb and oatmeal. Now after one feeding, she has complete diarrhea and I feel like I'm harming her more than helping her. Is it the rapid change in food? At what point does the diarhea subside? Petsmart's choices of foods are more convenient for me due to location, mail orders aren't really an option for me.Help is truly needed with this. Thanks in advance

Help with food choice