Re: better than Praziquantel

5cm sounds a little large for schistosoma, though possible. The largest females are of the schistosoma japonicum type and usually are up to 3cm in length. If you saw a ventral suckèr on them then it's a trematode (fluke) of some sort (e.g. could also be a giant liver fluke Fascioloides magna, Clonorchis, Opisthorchis etc.). Unless it's a fasciola type, then Praziquantel is still the stuff to prioritise taking.

Unlike other flukes, Schistosomes live in the veins around the intestine, and not in the intestine itself so normally would expect to see their eggs in stool and not worm itself. Though these things can go anywhere and probably could end up in stool if under stress and trying to escape from meds.

Do you have a travel history to east Asia or any other endemic areas at any time in your life? Note that the standard blood test for schistosomiasis used in most western labs uses African schistosoma "Mansoni" antigen and is NOT effective for detecting the Asian "Japonicum" form.