The size of your penis is inherited from your father, his father, and from your mother's male relatives. Also, your race has some bearing on penis size, as some races of men have really small penises, such as the Chinese, while others, like black African, Indian, or Arabic men, have, in my experience, really large penis sizes above 8 inches erect.
Your penis size increases from childhood to maturity as a teenager due to your body producing hormones that stimulate gr0wth.
The average worldwide erect member is 5.50 inches. Unfortunately, there are no herbal or pharmaceutical medications that will make your penis bigger. Surgical procedures have attempted to take it off. You may opt for a penile injection. All that this means is that you are going to allow the doctor to take fat from your abdomen area and place it in your penis. The penis hardly has any fat in it, so this could appear odd. If the fat injections shift, you may have to have surgery on your penis to get it corrected.
You have probably seen porn actors with 10-inch erect penises. These men are a very small percentage of the population and are not representative of what size your penis should be. Many straight women and gay males wouldn't have sex with such men, as it is far too painful.
There's always a lot of talk about "bigger is better," but most adults know that isn't necessarily true or even ordinarily true when it comes to "rubber on the road" usage. You may still continue to grow until around the age of 25, as that's when human development is really complete.
If you are overweight and carry a load of fat around your belly, then your erect penis will be hidden in rolls of belly fat, so lose weight and do exercises to get your stomach flat, and your erect penis will appear at its true length.
Be grateful for what penis size you have, as long as it gets hard for penetrative sex.