What Causes Lack Of Menstrual Periods?

Hi, I am 41 years of age and have just had a pelvic ultrasound done as I have not had a period for 4 years. My Dr has had blood work done which all came back normal. in 1999 I was diagnosed with PCOS however the ultra sound yesterday has come back with no overt features of polycystic ovaries I am type 2 diabetic and this was diagnosed 2009 and for the last 2 years I seem to put on weight but then it comes back doubled my GP has just changed my sugar tablets as my levels had risen in the last year so we are doing a 6 week trial on these tablets and will have another review My periods came as the age of 12 and have never been regular I would go up to 3 months without one and then when I did they weren t heavy but of a normal flow and would last up to 7 days. I had my son at 24 yo and from there my periods would go to every 6 months up until about 8 years ago where I had a period which was extremely heavy and was put on tablets to ease the flow, this was back in 2009 and since then have not had a period (wow I thought it was 4 years but doing calculations it s now 5 nearly 6) - I am being referred to to a gynaecologist at our local hospital but just want a little background as to why they have stopped ( I am not pre or menopausal either) - the conclusion on the report reads: Thickened and heterogeneous endometrium without focal abnormality - this could reflect hyperplasia and the endometrium is measuring up to 24 mm without focal abnormality or abnormal blood flow. Really concerned :-(