Gaining weight for IVF

Been ttc for almost 4 years now and going down the IVF route but I was told I was too light (BMI of 17 and ideally needs to be 19) so I’ve been having supplemental brunch shakes and eating more oats and nuts (no pun intended) and generally trying to increase my food intake LOADS but of the complex carbs type etc. This last couple of months I’ve gained 4 pounds! So happy! I have a ridiculously active job and I do yoga. Will start adding weighted exercises too soon I think. I haven’t gained weight in years!! Hope is starting to come back!