If you had your baby in January this year, I would guess your cycles are still a bit out of whack.
How long did you breastfeed for?
I got AF back at five weeks post partum, had three following that and then none for 11 weeks. It is possible that your body is just not rugular again yet.
If you are worried, sure thing, book into your doctor, but it's very normal to still be irregular at this stage.