Hi dear, Irregular periods
are quiet common with polycystic ovaries
which usually presents as amenorrhoea of 2-3 mnths.
In my view, single dose of sustain is not sufficient for withdrawal.
Also, with associated problem of endometriosis
, you ought to get fully investigated and treated including a diagnostic and therapeutic laparoscopy
Kindly consult a good laparoscopic gynaecologist and take full treatment