Just found out my 4 year old has undescended testes

Picked toddler up from school and after getting home he mentioned pain in his testicle. Waited a while before asking again because sometimes he’s silly and will just say things. Decided to take him to the ER where they did an ultrasound. No serious complications, but they did tell me he has undescended testes in the inguinal canal. The doctor said they will probably have him get surgery for it since the sooner it is done, the better chance for fertility. I immediately started googling after she leaves, and it says the chances get less and less for success after 18 months old for fertility and increase chance of cancer. Now I’m freaking out and appointment isn’t until next week. Anyone with similar success stories to help ease my anxiety?

Also, how did my doctors miss this after countless well visits?! I’m a first time mom and know nothing about scrotums. I had no idea anything looked different until searching. I feel like such a bad mom, but also angry with the doctors who have seen him. I went back on previous records and it says he had bilaterally descended testes at birth, they checked at 3 days old (same thing), then any other report at well visits said his testes were normal.

Just so upset and needed to vent somewhere ☹️