I'll add to this... I also started with F2F almost 18 months ago, and that then lead me in here... and then I learned about PM and switched after about 6 weeks. I dropped everything from the F2F routine apart from SP. My actual 'budding' growth started 3 months from the very beginning and after another 6-7 months I looked like my avatar

- small 36B
That was 6 months ago and nothing has changed since then, either by tape measure or the 'slightly too big bra' method.
So I have come to the conclusion that either I have stalled big-time, or I have actually reached maximum growth on PM alone. I don't think it is a stall, because in the last 6 months I have varied the PM dosage up and down from nothing to 3000mg a day and although I do get minor twinges as the dose varies the growing pains have virtually stopped (although the tenderness/sensitivity etc remain.). So I have a feeling that I may have reached max growth potential in terms of basic underlying structure. However I still have the triangular immature breast shape, so I have hopes that there may still be some potential to fill out and become more rounded. To do that requires the prolactin and I'm planning to switch to Isabelle's herbal routine in the near future to see what happens - I'm also hoping that if I'm wrong and I have stalled on PM, then the different combination may jolt me back into growth anyway.