What Causes Vaginal Spotting Along With Bad Odour?

Hi, Recently i was spotting really light pink and i would only see that when i would wipe myself. It had a really bad odor like a dead animal. The spotting only lasted about a day in a half to 2 days. This has never happened to me. I do have irregular periods, but only a couple of days off due to me being a type 1 diabetic. This did happen a week before i normally start my period. I have not yet started my period. Why did this happen?