I havent had my period in about 90 days but im a virgin and ive only had it twice before, and im 13. why is this? what do i do?

In the first year after menses starts, a young woman is often not releasing eggs, & this can create an irregular pattern. After a year or so, egg release is happening & the process usually becomes more predictable. Delayed cycles often lead to heavy and longer flow when they do happen. Some docs would consider using a minipill (BC) to help set a predictable pattern.