Never say never, & never say always.
If the pain is truly in the back it is unlikely this is related to diarrhea
. Most cases of diarrhea are from a viral infection & will usually pass in 24-48 hours. But prolonged diarrhea, especially with blood should be evaluated by a dr. There are many other variables a dr. Will want to know: how long the pain, what makes it better/worse, same with diarrhea.