It has several possible causes, including conditions or injuries affecting your testicles, pituitary gland or hypothalamus. It's treatable with testosterone replacement therapy
Improve your diet and perform cardio exercises along with yoga.
Yes, if your testosterone levels are too low then your doctor may prescribe testosterone replacement therapy (TRT) to you in which you may be given gel, patch or injection to raise your testosterone levels.
One can only know if you get a testosterone blood test done preferably early in the morning between 7 to 10 AM. During these hours, your testosterone levels are typically the highest.