I'm A 47 Year Old Female And Just About A

I'm a 47 year old female and just about a little over a month ago I started having diarrhea. It has not stopped. just got 4 stool tests done and they are negative for the common culprits. No, I have not traveled anywhere. I eat the same type of diet consistently. If it were something like IBS why would it suddenly start now after all these years???