1 year and 7 months ttc

I'm 20, classified as over weight, and so is my boyfriend of 6 years. He on the other hand is closer to normal on the scale. We have a 4 year old, we started trying for another child 1 year and 7 months ago, I go to my yearly OBGYN visits for physicals. I'm honistly done trying to have another child this year. In this year alone I have lost 2 people I cared for. One was a old friend and the other was my Grandma. My Gram practically raised my brother and I. Well getting back to the point I decided to confess to my sister that we were trying to have another one, and now I don't feel like I can talk to anyone about this issue because I'm afraid that they will say " your trying to hard" or "just be happy you have one". I'm trying to be. I love my son more then anything but it's hard when he sees a baby and says "mama I want a baby sister". I just need someone to give me hope. Sorry this is such a long post.