I am so sorry. How scary! I'm glad you persevered and got the diagnosis so your little boy can get fixed up. I get so angry at pediatricians who blame the mom or write off real concerns as "oh she's just a crazy first time mom who doesn't know what to expect." I experienced some of that with DD1 and know how frustrating and maddening it is.
Hugs to you mama! What a rough ride you have had so far. I know surgery will go smoothly and your baby will be gaining well in no time.