Does low sex drive mean low testosterone?

I have a low sex drive lack of morning erections porn doesn't turn me on anymore and I don't care about sex.I could live without it.I been feeling this was since I was 15 I am now 20.Yesterday I seen this phat but girl walk in front of me and I got a erection.And the only way I can keep a erection is with constant stimulation.If I stop masturbating it goes down like 2 minutes after.I also I have a 6mm pituitary microadenoma.