Not news I wanted to hear

So my husband and I just recently signed up for a gym to tone up a bit. I've always been a little too skinny, when i met my husband I weighted 110 lbs and unfortunately I lost a lot of weight going through his deportation and for the last 5 years I've been stuck under 100 lbs no matter how much I try to gain weight. Well last night we decided to see the nutritionist at our gym. He told me something I've heard almost all my life that I'm underweight, but he also told me something else that just crushed a pArt of me. After taking my measurements he asked if I have had issues getting pregnant. I told him recently we've been trying, and nothing  He told me that the reason I'm not getting pregnant is because the size of my lower stomach, it's supposed to be a 3, and in at a 1 (like the fat measurements)😔 I hate that my size could be what's preventing me getting pregnant. I'm hoping after going on his diet plan to gain weight hopefully it will be easier getting pregnant. At first I didn't want to believe that could be the issue but the more it sank it the more it made sense.