Hi there ~
I understand your concerns. It is very common phenomenon to consider your penis as being short and weak or your testicles to be unequal in size and it might be natural at your age. You do not mention your age, however you will do well by knowing that there is a range of normality when it comes to size of genital organs. If you are not sexually active, this would be the least of your concerns. However, if you want to get tested, a qualified psychiatrist
or a local doctor can help with investigations and other laboratory studies.
I hope this helps. Take care and have a lovely day!