First play in middle game I have a problem when I have developed all minor pieces and castled. The position looks perfect for me and my opponent. I don't want to move a piece since that would ruin the position and create weaknesses. Most often I end up with an unclear attack that works or not, i.e. I jump out and see what happens. Is this an unknown problem? Am I just lazy in calculating? Is there some good source to help me (drugs, books website, rules of thumb)? What should I look for? Should I think in some special order? Does this stage have a special name?
You're having issues with the transition to the middle game. I'm not sure what your current skill level is, so this advice is going to be a bit scattered.

First World Correspondence Champion CJS Purdy (Art of Chess Annotation vol 1 and/or Search For Chess Perfection) details a thinking process which consists of things to think about when on move and when your opponent is on move. Jeremy Silman (How To Reassess Your Chess) has a modified version of it. There's another approach in Alexander Kotov's Think Like A Grandmaster.

If your problem is more what to think than how, Former World Champion Max Euwe (with Walter Meiden) did a two-volume set (Middlegame) and the Soviet school was fond of a two-volume set from Romanovsky of the same name.

They all say it better than I can, but the tl;dr of it is that once you have completed development you look first for the tactical opportunities your opponent will give you. Everyone you play will give you those opportunities, you just need to be able to recognize them when they happen.

Sometimes there will be nothing specific to do. If that's the case, then proceed with a more general approach.

Try to "read" the position, the way a golfer might read a green; look for strengths and weaknesses in your opponent's position and your own. Your task is to weaken your opponent's strong squares, and use their weak squares to advance your pieces across the the center of the board. As for your own, you eliminate your own weak squares and keep the strong ones strong.

As you might expect, you can't do all four at the same time, so your thinking centers around what weaknesses you can exploit that will gain you more than you lose by exploiting them, and whether your own weaknesses can be easily exploited. (A weakness isn't real unless it can be exploited.) As you locate tasks (undermine this point, occupy this one with a knight, defend this) you'll see that some fit together into a sequence (can't occupy this outpost until I control this other square, need to defend this point so the opponent can't get around me, etc.) and that "sequence" is called a plan and you decide to follow it until/unless something better presents itself.

Kind of vague, I know, but so was the question.