Try recording the starting date of your periods and look for a pattern - count the days between the starting dates of your periods. Either use your diary or try one of the free phone apps for period tracking. If your periods are quite irregular after 5-6 years this probably should be investigated so I suggest you see your GP (you may be more comfortable seeing a female GP)You would probably get blood tests and an ultrasound. Depending on the cause, you may not need treatment at all so don't worry, no one will force you to go on the pill. You may also want to chat to your mum or a close older female relative.