Proper itemisation
tl;dr what to buy when behind
For a while now I've gone from 90+ LP (and promos a few times), to 5-game loss streaks losing nearly all of my LP. I don't think I'm a terrible player, but my op.gg MMR has tanked from 1300 to 1180 over the course of the last few days, so I'm probably at fault for all the defeats. I lose games even after I felt I was doing pretty well, but there's times when I make bad decisions because my team isn't doing as well and I fail to recognise when I should be helping them out rather than continue doing what I do. Sometimes I'm just the hopeless feeder, caught in a lane I cannot win and yet I struggle.
I upgrade my trinket (or upgraded, it's broken currently), and I tend to allow my team mates to engage when I'm playing a squishy champ. Whenever possible, I peel for my ADC, and I don't rush into 1v5s as often as I did at Bronze. (But sometimes I go full herp derp and barrel into I Regret My Decision Immediately-waters.)
I remain convinced I can depart from Silver III and climb towards Gold, even if my current results heavily disagree with me. However, the way I currently play I feel like I'm more of a detriment to my teams than an asset. Otherwise I wouldn't be having losing streaks so often. So I figure I'll turn to the boards for advice, since Google didn't help me.
What are items I should be buying when losing lane?
I tend to:
ADC: Ashe/Tristana Mid: Lux/Anivia Top: Hecarim/Ekko Jungle: Evelynn/Skarner/Hecarim Support: Leona/Soraka/Sona/Janna
I tend to do OK when I buy items because I'm going toe-to-toe or ahead, but my itemisation when losing is what I think could use improvement. Normally I continue stubbornly buying my items when I do get the gold, though as Trist/Ashe I tend to pick up a second Doran Blade. I do get health pots on every back until ~12 minutes.