If you have had regular 28-30 day cycles earlier, you should get tested for pregnancy
through a blood test
preferably as this gives a better conclusion. Condom has an average failure rate of around 15%. If pregnancy can be excluded, it could be a hormonal
imbalance that is usually seen at this age, provided local causes are excluded by a specialist. You may need hormonal supplementation. Please use a regular contraceptive
that suits you for better protection. Hope your query is answered. Good luck.