Would an infection from a miscarriage go away by itself or cause toxic shock or something?

Sometimes. Infections after miscarriage are uncommon but they can heal by themselves. We usually want to treat the infections with antibiotics to prevent scar tissue that could cause infertility or develop into an abscess. Toxic shock is usually not caused my miscarriage. If you are unsure whether you have an infection or you need treatment then speak with your doc. Best wishes.