Low test result but doctor doesn't seem worried

I am 45.
5' 9"
230lb
I have been battling with depression for awhile.
I have been feeling lethargic.
I now have no sex drive. I have difficulty achieving and maintaining an erection.

I asked my doctor to run whatever tests a man my age should take.
My testosterone came back at 122
The office called me. They didn't seem to worried. They set up another test in 3 months

They also gave me a sample of Viagra 50mg which did work on me.

As i did a little research I found that 122 is extremely low.

Do I need to find anther doctor?
Should I have them run some more tests before 3 months?
Is there any vitamins I can take to help boost my testosterone?

I'm definitely worried about this but also hopeful that this might be the cause of my depression and erectile disfunction and might be curable.