My son had this really bad, the shampoo's only worked to a point but they didnt get rid of it totaly.
the best thing i used was vaseline, is a bit messy but works so well!
put lots of it on to your babys head and leave it over night, the next day put shampoo right on it to, with no water, lather it up then wash it off with warm water.
took it all off my son and it never came back