Advice

Is it normal for my cycle to have no rhythm/regularity? For instance one month my cycle can last 36 days another month 39 days and another month 29 days?. I’ve had my period for 8 years now. Should I be worried. Should I see a doctor? I’m always on my period for 5 days and that never changes. So basically I don’t know when to expect my period. I Also don’t know what days I actually ovulate. Any advice would be really appreciated.