what happened to my penis? and does it look fine?

Well, I hope that anybody can help me with this. I didn’t have any problem with my penis until May 2019, after masturbating it swelled up, the following months keeps same thing, after ejaculate it swelled up. While occurred to me that my erections started to get weak. Now in 2020 my erections are stronger (not my 100%) but i feel like I have stretched skin there, also I have wrinkles on penis shaft. I’m 16 years old.

Ups, I meant “while it happened to me” instead of “while occurred to me”, problems of non native American

This is an interesting issue that you have, the health specialist that could help you most with this is a Urologist.
However, the most important issue is that you are 16 YOA and your penis is still developing - I think a Urologist would be inclined to tell you that you need to wait until you are 18 to 20 YOA and see how your penis is at that time before deciding whether any action is required.
What I would do is to explore the fun you can have with your penis without actually masturbating. Try something like a baby oil or lotion, or better still get yourself some liquid coconut oil and apply a very light coating to your penis and try the different ways in which you can manipulate your penile skin - do not use hard pressure or force, you are after more of a light massage action.
Concentrate more on this rather than how strong your erection actually is, or the need to masturbate and make yourself ejaculate. As I say, keep it pleasurable, explore different ways to manipulate the skin and use soft movements of your penis, up and down and sideways, back and forth …