First of all, you are probably ok. I don't know much about the effect of a fever on a fetus that small, but I'm sure someone here can offer better in-site. Hey, plenty of women don't know they are pregnant until WELL into their first trimester. MANY healthy babies have been born to moms who casually drank and smoked through the first two months because they didn't know they were pregnant.
I''m sure you'll be fine, but do run it by your doctor
[i]disclaimer: I am NOT advocating drinking or smoking while pregnant, just trying to make a point![/i]