P.,
My youngest son had a hydrocele when he was 4 months old, it showed up just after his checkup. It was really scary! Right away we called a nurse line and they don't tell you much ~ it could be a hernia, it could be that something is twisted or it could be a hydrocele. We, of course, freaked out and went to the ER. The ER Dr. did an Ultrasound and said it was a hydrocele and to watch it. Our 6 month check up came and we talked to our Dr. about it, he then told us he had noticed it at the last checkup, but didn't feel it was anything to be concerned about and didn't say anything to us!! ARG! Anyway, the hydrocele went away by the time he was 12 months.
It's always really scary when something is not right with your child, but have hope that it will all work out and it will.