Testosterone booster

Testicular cancer survivor having trouble making gains

I'm a stage 4 testicular cancer survivor having problems making and keeping gains. My testosterone is extremely low & I have a Dr appt June 16 to go over my options. What can you suggest to do to keep muscle & good weight on?

Would it be beneficial to have a slow digesting carb with my protein shake before bed? I am trying to put on some size and weight but don't want to have fat storage.