Can side effects when taking antiparasitics be taken as proof that there is an infection?

I have been previously diagnosed with pinworms and can present physical evidence of them, though people still seem determined not to believe me!
I've taken rounds of Ivermectin, Humaworm and Mebendazole and experienced fairly strong side-effects...I assumed that this is evidence of the drugs working and that therefore there must be something to kill, else nothing would happen.
Is this generally true or does it depend on the particular medicine?
I get a lot of denial thrown in my face so I'm just looking for as much reassurance as I can get that I'm not deluded!
What do people think?