Gold 2 last season having trouble in Silver 3

Lol, dont laugh ok. I wasnt boosted, I was Gold 4 in season 4 and tried for Platinum in season 5 but I got stuck at Gold 2 100 LP and lost the promos 11 times in a row. I don't even know how is that possible and then went on tilt and dropped to Gold 2 0 LP. Now long story short, that happened on September-October and lost my will to play until January. I played my rankeds and went 6/10 and dropped to Silver 3. The point is that I'm on a 50% win rate on Silver 3. How did I achieve this? I don't know what is wrong with me, I used to play vs Platinum and never had any trouble winning them and now I'm having trouble vs Silvers. I know that I pick random champions I rarely played before but even with them I can still play better than silvers and yet I lose. Went on tilt again yesterday, 5 defeats in a row from promo to 10-20 LP. 2 defeats becaused I played first time Jhin as adc ( Retarded Mistake ) and I dont know how I lost the others. Why am I still losing even when playing better than these guys? I have better mechanics, better CS, better map awareness and pretty much everything better and still lose.
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