What Causes Short Menstruation Cycles?

i am a 25 year old female, i lost my right and 3/4 of my left ovary to a dermoid cyst, by the time i was 15, i since have had 2 children. my periods use to be a regular 28-29 days apart and are now 20-22 days apart, could i be running out of eggs or going in to ealy menopause??