I take metronidazole and amoxicillin together. Possible side effects?

Yes. You can take these 2 antibiotics at the same time. All drugs have potential toxicities and side effects. Do not drink alcohol while on Metronidazole as it can cause an antibuse reaction. It also often causes a metalic taste. All antibiotics can cause nausia, vomitting, diarrhea, oral thrush, allergic reactions etc.