Is there any medicine I can take to increase milk supply?

You can try Blessed Thistle capsules. My friend isn't keen on medication/drugs so she tried these herbal capsules (2 capsules 3 times a day) and she found that it helped with increasing her milk supply. You can get them at Watsons/Guardian or order them online from iherb.com or kulily.com -- retailing at around 10SGD.