What could be wrong with my septic system. I had a new system installed 6wks ago. Now for the past month when the water is run I get a sewer gas smell in the house that will go away within 5 min?

It depends upon the venting that is used, look for your vent pipes on the roof and see if any are close to open Windows. If you find a particularly close vent pipe (and you home has several vent pipes) you can add a "Studor Vent" to the top of the vent. A Studor vent is the equivalent to a one-way air valve that only allows air to pass, or be drawn, into the pipe, so that sewer gases will be greatly reduced. You don't even have to use pipe cement/adhesive to secure the Studor Vent.