28 days isn't really the average cycle length - that's just what birth control regulates your cycle to so that's what most people think. :) It seems to me that people who are not on HBC have longer cycles, more like 30-36 days.

In any case, bouncing between depo and the patch and whatnot is probably causing your body to be a bit confused so you may have a delayed period, or even no period for a while. If you're concerned about pregnancy, I would definitely recommend taking a test just to know. :)