On Methadone and having abnormally long periods

I'm 38 and have been on Methadaone for pain for just over 2 months. I have and IUD and usually my periods are 5-7 days with 1-2 days of very heavy flow. Last month I had about 12 days of period, mostly very light -1 day of moderatly heavy. This month I am on day 18. 16 days of 'coffee grounds' rarely needing a tampon and 2 days so far of some of the worst bleeding in a long long time.
Any ideas? ---I Do have PCOS but previously no cysts
Thanks

How bizarre! I have month-long periods-lots of days just dark brown 'strings' and I thought it was because of my implant contraceptive but maybe it's methadone-I'd been on it for 3 months before it happened.....