I'm 23 and I got a small one

Your circumcision has nothing to do with it not having grown. Actually your size is considered average for adult males. The majority of men fall into the 4 to 6 inch range. One thing you can try is to lose weight. I don't mean to sound like I'm picking on you when I say that but carrying extra weight, especially in the abdominal area can overwhelm the penis and actually make it smaller because fat protrudes into the pubic area. When you lose weight from that area the fat will subside and the penis will be more prominent. Otherwise don't worry about it. There really isn't anything you can do to increase the size no matter what you hear or see on the internet. Remember that for a woman who has never given birth, her vaginal canal is only 3 inches deep when she isn't sexually excited and about 4 inches deep when she is excited. Given that, your penis would fill that space. I hope this helps!!

Thankyou so there really isn't a way for it to grow naturally other than losing weight. hopefullyI do lose weight and grow a little. is there any other thing I should know should I go to a doctor and ask?

Remember that losing weight will only make it more prominent and perhaps a little longer if some of it is being consumed by extra fat. You could go to a doctor to ask about help with weight loss but nothing else is going to help your penis grow. You've got what you've got and it's average.