I have low testosterone. I get injections every 12 weeks called Nebido.
Since I have been getting the injections my testicals has shrunk.

Questions. Is it because of the injections or maby my age? I am 45
Also I still have to use other medication to get and maintain erection.

Question Is there other options my doctor is maby not sharing with me that can improve my libido to want to have more sex and to better erection problems

Testosterone injections can shrink the testicles, because the injected T actually decreases the naturally produced T in your testicles.
More is not better - there is evidence that excess T injected is converted to estrogen, which in men will decrease libido.
Getting T in conjunction with taking Viagra or similar drug is considered a good combination overall.
Your doctor could possibly attempt to offset testicular shrinkage with human chorionic gonadotropin, or HCG. It may also boost adrenal functioning, libido and overall energy.

Avoid all the thousands of products you can buy over the counter.