Please consult a urologist to find out if both your testicles are working fine. As regards the bone density problem, it may be a case of calcium and/or Vitamin D deficiency, you should get a blood test done for better evaluation.
I would get those testicles checked out ASAP that really doesn't sound good and for trying to last longer during sexual activities, I would personally try the "stop, start" method so masturbate until you reach the point in which you think you are about to ejaculate and then stop before you do wait a half a minute or so and repeat until you can't keep going over a period of time it should help it did for me hope you get yourself sorted out bro
Ejaculating in just 4 seconds is a serious concern. Please practice masturbation regularly
ejaculate in 4sec! UNBELIEVABLE
Don't masturbate everyday. If your testicles are in fact a 1:3 ratio and your left one is 3x larger than your right, than that could be a problem. I don't think that is normal. They should be roughly the same size, one can be a little bit bigger I believe. How do you know that your bones are weak and brittle? And how do you know that you have a low bone mass density? were you diagnosed?