Is it normal if you used to have a perfect 28-day cycle but after being on Depo-Provera for 3 years you are now getting periods every 14 days?

You are probably experiencing breakthrough bleeding which can occur while taking any Birth Control. You may want to alert your doctor but this is not abnormal. I found that when I stopped taking the depo shot, which was Feb 2005, and I was only on it for 6 mnths I am also getting my period every 2 weeks and my cylce was every 28 days as well.