You definitely need to see a doctor. If blood pressure isn't the problem, then something else is involved. A couple possibilities are prostate problems or a pinched nerve in your lower back. Start with your family doctor and tell him exactly what is going on and take it from there. Your family doctor can get you to the correct specialist so you don't waste time and money muddling about from one doc to another while getting no real answers. It could also be a simple matter of normally declining testosterone, which a blood test will tell you in short order, but wouldn't explain the back pain. Bottom line - get yourself to your doctor. :-)
You might want to see about making an appointment with a urologist. It could be just the aging process.