I was diagnosed w IBS from a lower colonoscopy. I have been living with diarrhea over the last year. Now I have a rash all over my skin & lost weight?

Probably not related. .... unless you were given a prescription drug for the IBS that may be causing the rash. Important clues about what might be going on will come from someone looking closely at the rash and taking a diet and symptom history to try to ascertain why you might be losing weight. Keep working with your doctor to sort through these significant problems. Best wishes:)