My cycle started on 12/14/21 and ended on 12/18/21. my doctor go my blood work back on 12/22/21 and notify me that i was vitamin d deficiency. i started trying my vitamin d supplements on 12/24/21 which i only take once a week. i started bleeding?

I doubt the association between a loading dose of vitamin D and vaginal bleeding but I cannot rule it out. If you just have a short vaginal bleed, ovulation bleeding seems fit the timeline.

Vitamin D supplementation and bleeding are unrelated. Menstrual irregularities are not uncommon and anovulatory cycle is a common cause. If you do not wish to be pregnant, use contraception all the time, consider implanted contraceptive or an IUD. http://www.nichd.nih.gov/health/topics/menstruation/conditioninfo/Pages/causes.aspx