Spotting and redness

My baby has this kind of spotting around his neck, chest, back of his ear and even chin. There’s patches of redness around his arm too. Have been keeping and making sure there’s no milk underneath his neck folds every single time and always pat dry every folds after shower and feeds but it seems to have spread to other areas.. His redness patch on his arm appeared 3 days after his vaccination but it was given on his thigh.. could it be allergic reaction ?#1stimemom #advicepls