Irregular Cycles are doing my head in

Okay so, I'm having cycles that can range from 35-75 days! my menstrual cycle generally also lasts two weeks, I'm so tired of dealing with this. I'm getting rashes downstairs from wearing a pad too much! I have an underactive thyroid also, I've been checked for pcos but not thoroughly, I've been told I've had no cysts but then I've been told i have them. I need a doctor that will listen to me. :(