In some cases where genetics probably play a larger part of high SHBG, increasing your Testosterone may not lower your SHBG – it did not for me.
You begin looking at other possibilities Danazol (using now), Proviron (didn’t work for me) and Clomid (never tried).
If you are genetically disposed to high SHBG, there is no such thing as “looking for the cause of your high SHBG”.