Hello Liranm!!! Shalom! (Don't mind my little bit of Hebrew. I always like trying out the little bit that I can. My wife studies Hebrew very much as a hobby. I actually speak Arabic, and although the languages are completely different, I still find the gramatical structures and some of the words very similar.)
Well, I have to say, for being self taught you are quite a wonder! In any case, I don't think there is anything "wrong" with the way you play. It does get the job done, yet looking at your video, it seems that you are straining a bit. Is your hand at all tense? I mean, you should keep your hand steady, but at the same time you cannot force it. I am only going by what I see in the videos, but I can actually see muscles in your arm flexing. This is a sign of tension. But, it could also be that I am judging badly through the video. Well, anyways, enough talk and more to the point. Here is what you can do for the perfect hand position: First, lay your arm over the guitar, resting your elbow on the guitar as would would normally, but completely relaxed. Just sit there a moment without any energy in your arm at all, letting it almost hang. After this, bring the arm up over the strings without any tension or using any muscles. This should be the perfect hand position. When you start to play, it should be as if you are "zapping a frog with a battery," the "frog" being your hand. The right hand has to be "as dead as fish, that still moves"(Don't mind my analogies, they are crude but get the job done when explaining) There should be little jolts of energy in your hand, yet between each one, there has to be a feeling of complete relaxation. It wouldn't hurt to even take a few lessons to set yourself straight in any case though.
Remember, when you change something as significant as hand position when you play, it may seem a little foreign to you at the beginning. In order to overcome this, you must practice incredibly slowly(slow-motion) and go back and do some simpler pieces(not necessarily tremolo, for this require a perfect hand position already and it does not allow you to concentrate at the problem at hand). Just remember, sometimes, in order to jump forward, it is necessary to take a few steps backwards first. Great luck and keep up the wonderful work!