I am 23 never had sex and been tested and have no std but some months i notice i miss my period what's happening?

Normal variation.: It is not uncommon for a woman's menstrual cycle to vary from month to month, or skip a month entirely. Stressors can cause your body to skip a cycle, such as severe illness, extreme exercise regimens, being radically underweight (i.e. Anorexia nervosa), or high amounts of emotional stress. If you are concerned, see an ob/gyn doctor who can run tests and check for any problems.

Missed menses: Obviously, would want to get pregnancy test dysfunctional uterine bleeding is term for non-ovulatory cycles which is common cause of missed periods at your age.