Where would i stand sueing a doctor?

hi my son is only 4 years old and last week he was complaining about a sore throat and on saturday the 18th of june i noticed he had a rash on his chest and back, so i called my neighbour over to have a look and within minutes or even seconds of her being over here he had spread to his elbows so in the time frame of me getting him to the hospital in 5 Minutes it had spread to his face behind the knees and the groin. i took him to casualty and i told the doctor how fast it had spread and he could see for him self that it was bad so he looked in his mouth and seen his tonsils had swollen and the rash was pretty severe and he turned around and said it was either a allergic reaction to some thing or viral infection? and i asked them what? and he said i didn't know so they gave him some Prednisolone and phernergan and sent me home. so i got a second opinion and that doctor said the same thing over the phone, now my sister is a nurse and she said i think it's scarlet fever go get his throat swabbed so my sister took him in on the monday 20th of june at 12o'clock and that doctor said the same thing i don't think it's scarlet fever he doesn't have all the symptoms but did you want to do the swab anyway? and she said yes it would put his mother at ease so he did and i get a phone call of the test tonight at 6.30 22nd of june saying his test results came back positive!!!! so the doctor didn't even send him for a swab at casualty where the law is to do some tests and he didn't so if it wasn't for me demanding to get his throat swabbed i wouldn't have known. Now scarlet fever can cause heart problems later down the track and you dint know if it has done any damage to the heart until they get older like 16 years of age so it has taken them nearly four days to put him n antibiotics where they could have put him on antibiotics in 24 hours.scarlet fever is very highly cautious And i have a 2 year old daughter so he on;y hasn't my my sons life at risk he has put my daughters life at risk he had 2 of the symptoms where you dint need all of the symptoms to have it. So please help me me where would i stand i want to sue them after them misdiagnosing him for the wrong thing and not doing anything about it at all until i had to demand it where i shouldn't have done that at all. They are doctors our lives are in there hands!!!! it could have killed him in the Long run if nothing was done and the doctor i seen wasn't going to do anything at all