Is fever after every vaccintaion normal? does it signal a weak immune system? i'm concerned because my son always seems to get one after a shot.

Depends on vaccine: Not all vaccines cause fever, some more likely than others. For example the Dtap vaccine and the VZV and MMR vaccines which are live vaccines are more likely to have a fever associated with them. It does not signal a weak immune system, in fact it most likely means the pt's immune response to the vaccine is good. Treat the fever for its uncomfortable symptoms.