Gargy,
what happens with PCOS is that your body is less likely to behave as predictably as someone without PCOS so that sometimes you might understimulate but next cycle, overstimulate on exactly the same dose. For a person without PCO, the dosage of FSH varies according to age and weight but then with people with both PCO and PCOS the FS has to take that into account and adjust the dose. Typically for a first cycle they would generally tend to give a lower does as PCOS people are more likely to overstimulate and be at risk of OHSS.
I am not sure if they use the same dosages with IUI as they do with IVF, as they don't try to get as many eggs with IUI but to give you a comparison, my donor was given 300 on her first cycle and my FS says that is the typical dose for a person of 35 years old.
Sounds to me like your FS was making sure you would not overstimulate when giving you 150, as that is more of a typical dose for a person in their 20's rather than their 30's so my guess would be he will start you off on something higher this time.
good luck.