Can't win even in silver 2 anymore.

Plenty of possibilities:

1. You haven't played ranked for a while and so you've forgotten your basic game mechanics.
2. You're not playing the champs that got you to G3 in the first place, or those champs have been nerfed/don't work as well in the current meta.
3. Your Elo is still feeling the effects of the ranked reset - you're competing with other low Gold (last season) players meaning that you're finding it hard to win games and increase your MMR.
4. You haven't yet adapted to the new Season 6 changes.

Overall I wouldn't sweat it. Just play the game for enjoyment and improvement, and you'll naturally reach higher tiers.

Soft reset bud

It all has to deal with the recent reset. A vast majority of the player base is in Silver right now, Gold is top 20% and Plat is like top 8%. You'll get back into gold easily by the end of the season.

It also highly depends on your team. You can't carry them if they don't pull their weight.

Here's a good example. My last ranked game I played Jinx. My support was alistar. Up until the enemy Diana's first gank, he did a good job warding and keeping me healed.

What I didn't realize, is that instead of rushing sightstone and getting more vision down, he rushed the first upgrade to targons. The blur side first bush in bot lane was not warded and I used my wards for the jungle. Diana sat there until alistar engaged. We got behind quickly.

On top of this, our Malphite top lane rushed frozen heart against nasus. During the fights, he melted. The enemy team had no attack speed dependant champions. They had corki, Diana, Ahri and Leona as well. No attack speed to slow down. Our team had noone to hide behind when they sieged our mid lane.

Get the gist here? This is a team game. Not a "every man for himself" game.

Maybe you'll start winning in silver 3 or 4!