if your son is 4 months old then i assume he has already received to doses of DTP Hib and 3 doses of Opv.. if this is the case then you can recieve the same vaccine
that was given to him previously if he never had any reactions to those vaccines..
if this is the first time you are going for vaccination
then yes there is vaccine called DTap ( only the pertusis component load is low and is acellular) the main advantage is that this injection causes much less pain compared to DTP and also the magnitude of side effects like excessive crying and swelling of the infection site are also less.. and now a days thinner needles are being used to make it much painless..
coming to fever
component, its not a bad thing.. now it is beyond doubt that after a vaccination if fever occurs it is an indication that vaccine was taken up and body is building a good defence against these diseases, so even fever medications are not adviced unless fever is very high so that is not an issue to worry about..