Talk to Gynecologist on Delay In Periods

I had vitamin D deficiency so I started taking vit D softgels small doses everyday. My cycle starting increasing from 21 days to 25 days. Last month, I took high dose 5000IU but for two days only until I realized high doses are not to be taken. I stopped and started taking Boots Multivtamins A-Z everyday. Now this month's periods are delayed and cycle length increasing to 30 days. I have stopped multivitamins from past two days. Please guide what to do. I am 30 years, married with one kid, pregnancy negative