My DS had it when I was in early pregnancy. I had looked after kids with it and have worked at the Childrens Hossy so I was fairly certain I was immune. I just took myself to the doctors and had an antibody test. If they don't know what it is (and many don't I found out), tell them you want an immunity blood test for human parvo virus. I'd probably even give your midwives/caregiver a call and get them to write you a path form.
Most people in the community have had some contact with this disease previously and are therefore immune, even if they've never had it.
It has a really wide contagious period that is generally before the rash comes out.

My sister's daughter also had it in her third tri but as far as I know, they just checked her immunity and told her to keep an eye on any symptoms. Your bub is fairly well developed. I was concerned about high temps in the first tri but by the third tri I think you're pretty safe. All organs and brain are developed and bub is just weight gaining.