I am 18 weeks pregnant and think i've been around a child with fifths disease. what should i do. will my baby be hurt?

Depends on situation: Most of us have 5ths during childhood & develop lifelong immunity. If you did, you have nothing to worry about.If you were only exposed to the case after the kid had a rash, the kid was no longer contagious. If exposed in the days before the rash you may develop 5ths & it can hurt a fetus. There is no treatment available but close contact with OB is advised.