I understand your concerns.
A 5" hard is quite sufficient a size to have sex.
Secondly the size of the penis hardly matter when it comes to satisfying your girlfriend.
There are no medications to increase the size of the penis.
Sp please be so much bothered about your seize of penis and do enjoy your life.
If you still have a problem do meet a psychiatrist
who can advice you how to deal with the problem.
Hope I am able to answer your concerns.
If you have any further query, I would be glad to help you.
In future if you wish to contact me directly, you can use the below mentioned link:
Wish you good health,
Dr. Srikanth Reddy M.D.