500ml??!! looks like i must quickly buy oatmeal??!!! mai tu liao..My personal take is that any drug you take, even if they are said to be safe for nursing mothers, just dont't take in the long run. If gynae says take for 10-day period, then make sure you dont't go and top-up for more after that. Unless a few months down the road you need again then you can get your own supply again.
For me, Fenugreek pills/extract/tea all dont't increase only maintain. Probably increase 10ml after I take them for a week. The Organic Mother's Milk tea also contains Fenugreek along with other ingredients. Also, there is some controversy regarding the use of Fenugreek to boost lactation.
Other methods you may wish to try is to take oatmeal. Heard from a mummy that she took and can pump 500ml in one session! Also try to eat a lot of fish. During my confinement month I had fish for every meal, and within 3 weeks my milk supply established.