Megestrol - How long does it take for this drug to take effect?

What is it being taken for?

My personal experience- My obgyn prescribed Megestrol 40 mg due to constant heavy bleeding. She advised me to take 1 when I picked up the prescription that afternoon and another 1 right before I went to bed. She warned that if my bleeding didn't stop by the next morning, to call her immediately. However, after I took the 1st pill my bleeding subsided considerably. When I took the 2nd pill that evening, I was hardly even spotting. I called my obgyn in the morning to let her know the bleeding had stopped and I was already feeling better.
NOTE** I have ALWAYS had irregular periods. For years my cycle was like this: Sometimes I wouldn't get a period for months. Then IF/WHEN I did, it lasted 2 months. This was normal to me. I know now that my body was not producing enough progesterone. I kept my remaining Megestrol 40 mg pills on standby whenever I got a heavy blood flow- we're talking about LARGE blood clots and changing pads at least once an hour. When I was at 6 or 7 days of heavy bleeding, I would take 1 pill and it would help stop the bleeding. However, since doing some research about low progesterone (and I do not want to be on birth control), I am currently trying to change my diet & eat foods that help my body produce progesterone.