M., I'm so sorry that you're going thru this!
It sounds kinda like the end april when my little one ended up in the hospital for dehydration... She ended up having the "stomach flu" for 8 days... They ran all sorts of tests and thats all they could come up with.. They put her on iv fluids over night and most of the next day and let us go home cuz she was doing better, but then she just kept throwing up and i ended up admitting her the next night again.... It was the most horrible experience i've ever had. So I can definately sympathyse with how hard it is to see your little one so sick... Mine just kept throwin up anything we tried to give her, even pedilite and just had the diarrhea twards the end.. My docs told me to feed pedialite only till she kept it down. then after that, gradually give a little more.. My little one acted like she was starving all the time and just screamed, but when we gave her what she wanted, she'd throw up again... so limit the intake, but keep it consistent.. some each hour or two.. (of course this was all for a 10 1/2 mo old so it may be different for diff ages.) but really the only thing the docs could do was the iv fluids when she got tooo low.. and the little one just has to see the flu thru its course.. which is infurating-- shouldnt modern medicine have some miricle medicine to just fix it immediately?!! i wish they did!
i was told salmonella will make ya sick from an hour to 12 hrs after.. but that it runs its course in 24 hrs.. so i wouldnt think this was any type of food poisoning..
so i would say keep givin pedialite, keep in contact with the doctor, and look up dehydration on webmd.com and go with your gut instincts.. don't wait too long to take him in if your gut is tellin you this is not how your son is normally.. dehydration is serious stuff.. And this long version of the stomach flu just plain SUCKS!!!
Good Luck!