Absent periods!

Ever since my first period i have been irregular and when i was 16 i went to the doctors to get it all sorted they did tests for PCOS and signed me up for weight loss classes once i started loosing weight my periods came back and were still irregular but i had more than the reccomended amount a year. I got the implant in august 2013 and had one period in september. I then got in November . Since then no period apart from the time when i took the morning after pill in april. Anyone think it could be my weight, possible PCOS or because i had the implant ... Please i need advice and help!!