We had a lot of solar heat gain in our Den from the west side windows.
It's been reduced by about 85% using a couple Solar Screens.
http://ecorenovator.org/forum/renova...n-project.html
When the sun was allowed to shine into that area, it heated up the interior,
and of course the interior walls will pick up some of that heat (re-radiated).
I wonder if you have siding on the house?
I have found that vinyl siding with foam insulation installed under it, works pretty well.
I think ours is about 1/3" thick with aluminum foil to reflect radiant heat.