PCOS and underweight

Hey I've been TTC for just under two years now and found out I have PCOS the beginning of this year. I am currently seeing a naturopath and  she has put me on a gf and df diet with all the herbs and stuff to help (which it is) but unfortunately that made me lose more weight as I no longer can have dairy or carbs (well very little carbs). She and my specialist  agree that I need to gain a little bit of weight to help. Any one have the same experience (as in PCOS  and being underweight) and have any tips on how to gain weight?