On my ranked account, i tend to focus on a set amount of champs per lane, i usually have like 4-5 champs i can play per lane. What i am seeing in your history is lots and lots of random champs besides when you play teemo, which is a problem in itself considering you have to carry with teemo, not just be there since he can't tank, engage, or cc besides his blind. Hes a hard carry champ, who only works against certain champs like Darius and various other melee bruisers.
Try to stick to a few really good champs, and get really good with them, your cs is a little bit behind, but it's to be expected if you are countered.
I know in Plat 1 my teams usually trade champs so they can avoid the dreaded first pick counter thing, so maybe a little coordination in champ select would help with being countered which would help your CS.
Your items i assume are based on you who are fighting, so i understand why they are inconsistent, but i do agree with kennen doesn't need a Tri force xD.
I didn't look at your runes, but just make sure you have runes for the champ your trying to play, ADC's needs attack speed quints and AD reds, AP mages need magic pen, tanks need either scaling health or flat armor, etc, just rune for the champ your playing.
These things should help a lot, but you also have to realize that games just aren't in your control, i know iv'e lost shit tons on my main account, and most of the time i go positive, while the rest of my team has died 6 times in under 10 minutes before i can even roam to help them. So matches like that just suck and there's nothing you can do about it besides lose and move on to the next one since most plat matches are over in fucking 15 minutes.
Keep a good attitude and keep trying! GL man!