Three are several conditions where a woman only ovulates randomly. With a cyst generally pain onsets. However, if you get a period three times a year there is an issue with your cycle. There are other issues which need to be checked since you are 26 and not having a monthly period. I would not issue yourself a diagnosis. See the gyn or try your local planned parenthood or gynclinic.
www.plannedparenthood.com. This could still be a result of the Depo shot but need a full answer.