AF came 16 days late! 1st time

My Af came 16 days for the 1 st time .. Im usually regular but in december i was 5 days late do im not sure whats going in with me .. Ill probably make an appointment w/doc .. Just been a little disappointed and frustrated as ive been ttc for about 6 months now .. And not sure what to do .. Should i buy an ovulation kit?