As you say, your girlfriend is happy, you're happy, so what's the problem?
It sounds like you may be worried that your penis is somehow inadequate. Men get so many messages that everything has to be bigger in order to be better; for instance, bigger wallet (more money), bigger car (more power), etc. It’s no wonder many men think their penis has to be some mythical length and girth as well.
Penises are like noses: everyone has a similar one, with some variation. There are very small, pert noses, and very large, important noses. But they all work just the same. A penis may be on the smaller side, but it still functions just as well—AND gives its user just as much pleasure.
Most men erect to between 4” and 5”, with some variation. Whatever size your penis, it can bring both you and your partner great pleasure, especially when combined with accurate information and good communication. It’s the penis you’ve been given, so relax, value it, take care of it, and it will serve you well. Good luck to you. Dr. J
If she is happy, why worry?
sorry brother there is no way out to increase penis size. average penis size like mine is 6 inches but it doesn't matter. if your girlfriend is happy then do not care about it. in kamasutra there are ways to increase penis size but such kind of herbs are not availble these days.