thinking our son got CP for one reason and then 2 years later finding out its not that.

Hi my son is now 2 with CP and I'm now pregnant with my second child. We were always told that he had CP as a result of swollowing to much meconium.
I went to the hospital this week to chat about baby number 2 and they said they will do anything we want. Fine no problem as long as baby and myself are looked after. They then got the notes from my first birth and the lady said that the chance of my son swallowing that much is very unlikely as it was just under 6hrs from my waters going and me having him and it also said when they were examining me my waters where clear. She then read on and saw that in my discharge letter it said there was a chance I could of had an infection but she said that was unlikely too in the time frame, I was never told about that till she told me and I was never tested for any infections. I now have no idea why it happened, we know there where issues with gases. I want to know why we were told one thing and its now not that.
Any ideas on what I do now? I don't feel like its acceptable at all.
Very hurt and upset.