period gone messed up

I used to get my period every 31 days and ovulate around day 15, all was normal with November cycle. December cycle didn't show so went 73 days without a period then finally showed up. 
Now again I'm on cycle day 42 and no sign of af showing up, I've got no idea why it's gone like this for. 
What can I do to get them bk normal?
Been to doctor and hormones are ok, thyroid is ok. No weight changes