You want to follow up by not bug.  A great rule of thumb is to do two follow ups, one week or two weeks apart.  Wait one week after an interview and follow up.  Then follow up again one more time two weeks later.   It can be a bit of a tough situation as you want to chase the positions but you don’t want to bug them to the point that they don’t want to speak with you.  Even if this position does not work out, you want them to have a nice memory of you and you never know when something might open up down the road.