My private part (penis) is getting smaller day in and day out. I'm getting scared seeing that people in my age range are not like this. (I mean their own penis).
Please enlighten me the more.
The penis is a variable size organ. It's size at any moment depends on the amount of blood flowing into it verse the amount flowing out. Technically the penis can't shrink as far as the amount structure present, but it can appear to be shrinking.
Consider this image on the right. Which center dot is bigger? The actual answer is that the two center dots are the same size. You can prove it to yourself by measuring. The problem is that humans tend to judge sizes relative to what they see around them instead of by actual size.
Therefore, a boy's penis before he begins puberty might appear to be shrinking to him because his body is getting bigger but his penis hasn't started developing yet. Or if you are comparing yourself to other boys who are developing and you haven't started developing, it appears that your penis is getting smaller in relation to the size of the other boys' penises. Also when a person gets fat, he might think his penis is getting smaller but in reality it is the surrounding area (his stomach) which is getting larger.
Getting fat has a secondary impact on your perceived penis size. A portion of your penis is actually inside your pelvic area. It provides the base to hold an erection outward. When you are skinny, you can see a lot of the length of your penis, but when you get fat more of it is hidden underneath the layers of fat so it appears to be not as long. It is still the same size but less of it is now outside your body.
Since the size of the penis depends on blood flow, a person with certain diseases which impact the flow of blood will have smaller erections and even a smaller flaccid penis. For instance, type II diabetes interferes with blood flow to the extremities. A man having problems with clogged arteries will likely first see signs of it in smaller erections and difficulty in getting and maintaining erections. Even physical damage such as a blow that causes scaring tissue to form inside the penis can hinder the blood flow and thus make it appear to be smaller.