An average healthy menstrual cycle is 28-30 days..when this is lengthened or shortened it creates a hormonal imbalance.So you will need to get them tested.and if possible a scan too.
Next Steps
I understand that from where you are to get a lab test you need a prescription from a doc ,and if you are worried on having hormonal tablets.you may tell your doctor you do not want to take any medicines unless the reason to the condition is found.
Health Tips
Ayurveda had wonderful results in such scenarios but a basic test is always necessary