Well, part of the problem is you're an actively passive ADC. If I see that, I'm zoning the crap out of you if I get the opportunity. And if my support is on board, you're not seeing any farm for a few minutes. Long story short, you need to start learning some aggression. Obviously, don't just throw out random skill shots, try and punish them for farming. Watch where they and their support are, and try to force them to poke/trade you while inside of your minion wall. If they attack you or your support in that range, they'll draw the agro of the minions and at low levels, those minions hurt. See what minion they want to hit, try and position yourself to hit them when they step in to AA it. Keep in mind of what minion you wanna hit and watch if they're getting ready to punish you for it.
Sometimes, though, you have to back off and can't trade with them. Either because you don't have a support(yoloqq, yoooo), or they're hyper-aggressive and have the combo to do it. If you have to lose farm, you lose farm. Do your damndest to keep in range for exp without giving too much up(like being open for a gank, or them to all in you). Experience is just as valuable as farm. You can come back from being down 35cs, you have a much harder time coming back from down 35cs and two levels.
Going off na.op, you don't appear to be an adc player though, so you're going to get punished hard by adc mains, however. Pick a couple safe ADCs and learn them, and learn them well, if you're making a move to botlane. Caitlyn and Xayah are fairly safe. Caitlyn because she has that consistent range, Xayah because she has a pretty decent range for ADCs as well as good CC if you use it right. Trist is fairly interchangable with Caitlyn, but starts with lower AA range. Avoid the immobile hyper carries like Kog'maw, Twitch, or Jinx(Jinx is essentially low-elo Twitch, apparently). Practice your last-hitting in practice tool. Just trust me. Watch some ADC streams. Positioning is entirely the key as ADC. Non-adcs see it as a stream of long-range crit burst BS. Actual ADCs see it as a constant check on their position against everyone else's.
Once you can consistently hit 160-180cs in 20m in practice tool, do it again without buying your BF sword, or zeal items. Gimp yourself, pretend you're down on farm. The point is to practice actually last-hitting. Learn how to farm under turret. Melee minions> tower, tower, last hit. (this becomes harder as the game goes on if you don't have some sort of extra ad beyond your Doran). Caster minions> hit, tower, last hit.(this is only applicable when you only have your Doran's blade. Once you have any AD items, you should be able to last hit off the tower hit on casters). Then you can start working on trading and farming. You now know what you're looking for, you know what they should be looking for, you can then start working on positioning yourself to contest their farm, and position yourself against them contesting yours. Don't take my word as law, though, I'm just a lowly silver ADC. :3
