Why is my new house making me sick?
Exhaust fans are made out of metal and plastic.  Very very hard for mold to grow there.  Mold will pick out a more organic material - like drywall.  You should clean your exhaust for dust every year or at least check on it but not for mold.

I doubt if you have symptoms coming from your house that it is your exhaust or attic.  Now attic could have mold - I don't know - but it wouldn't have a great affect on you unless there was air blowing into your house from attic or the problem was absurdly bad.  But going up to the attic is 20 mins of your life - so just do it so you have peace of mind.

I would look at the shower area or ceiling and then check out other parts of the house.  I wouldn't discount it being something other than mold either.