Something is draining my battery

I have a 06 Chevy Impala SS V8 engine. For about a  
month now when starting my car I would have to
hold it in start for a few seconds for it to slow drag
start. But now every other day sometimes twice a
day I have to get a jump. I've had my battery
alternator and starter tested and they came back
fine anything that has to do with the battery
connections and all I've had it looked at.  But I was
told that it may be my starter draining my battery.
When I go places I just leave it running cause I'm
afraid it may not start.