(2) I figured out that most of my players had already played more than 40 matches! (i repeated the same team many times on all tournaments - and it explain the same what happened to one of my friends). Maybe it's something that could be tested!! (as you did switching your GK and ST)
Yes, that's an important reason.
There is some kind of season's fatigue.
It's good to have (not much) 4-5 bench players and do some rotation, specially in some easy games.

(1) There is some kind of wave of form, that no matter what you do, your team will lose straightly (and was exactly what was happening. i had already 5 losses in a row!)
Doesn't happening very often but there is. I don't know if it's some hidden calculation from the game
Another scenario is that some key players come together at a "de-form" period and this affects all the team's performance.
Usually it's the GK, a MC, the AM_s or the players you use for F-K or C-K.

(cause my team was like a plane going to crash a mountain and i needed to save it haha).
yeah, many times we feel that way.
You don't know exactly what is the right way to save the plane but whatever drastic you do, might helps.

when i was using 4-1-2-1-2ND
I suggest to find some other formation, better V style or something you can attack from the flanks too (like 4-1-4-1, 4-4-1-1).
Besides the forum, I 'm also in some T11 fb groups so I can see many "super" players.
Usually are wingers.