eruption of skin

Hello doctors, I’ve a girl who is about 11 months old, she have had a recurrent appears of vesicles on her body .It occurs in all over of his body in recipol manner .and some time it appears as pustule also and it goes erosion . usually it last about 5-8 days and then gone . moreover she had some allergic from some milk and som foods also in our family we have allergic history. so, I need to know the Dx. coz I was thinking it could be measls but measls must be preced by U.R.T.I. and appears in neck or behind ear thats way i said is not measls or chickin pox coz i know it to . and shall i give her antihistmaine does it help ?? plz answer me