In my experience Drs will not investigate until you have gone 6 months without a period. I came off the Pill in May 2010, had 1 period in June and then nothing.
I went to my GP in September and was told to come back in January. Multiple blood tests, ultrasounds and an HSG later they diagnosed PCOS which had, as you say, been masked by the Pill.
I'm now on my 6th, and final, cycle of Clomid. I've been lucky that 50mg has been enough to make me ovulate, but sadly I am still not pregnant.
I am also slim and, barring having the skin of a puberty-ridden 13yo, have none of the other "classic" PCOS symptoms.
Do keep pushing your Dr to send you for more tests. GPs know very little about fertility issues, after all the nature of their job is to know about lots of different things and not specialise in one area.