Thank you for your question.
If this is the first time this has happened you need not worry. If you see your gynaecologist they can examine you to rule out other causes and provide you with a prescription so you can get a bleed. You may benefit from keeping a menstrual calendar to see if the problem recurs or gets better by itself which it usually does.
Your gynaecologist can provide information based on whether you wish to conceive or whether you need reliable contraception. Both these circumstances require an assessment of your menstrual cycle and the calendar you keep can be useful.