Irregular period (Nexplanon)

I've been on Nexplanon for a year And a half now ... And ever since I have started Nexplanon my periods have been very irregular! Last month I didn't have a period .. And this month it started on the 1st and ended on 26th. My question is , "On what day did I ovulate this month?" Because idk because my period isn't regular anymore. Or .. "Do I not ovulate because I'm on Nexplanon?" Help please. Thank you.