when did you get your positive result? have you been plotting temps or anything that may give you an indication?
and what do you mean they cant fit you for in a couple of months? have you seen a midwife? 12 weeks from conception is first scan date so max 2 months from when many women get their positive.
I also have PCOS and Im trying for a baby, when I went to one of my hospital appointments I asked the very same question (getting prepared lol) but was told that it is very difficult to pinpoint how far gone you would be until you get into a cycle,Im now on Clomid so will be a bit easier.Have you been on any medication to help you???