First you must get lvl 11, you can farm quickly with mushroom (+400 damage kills all small minions)
and your enemy won't jungle anymore :D

No!! you are not weak, After you got rabadon's deathcap.
and; you don't need Void Staff or another AP item

Blinding Dart: lvl up to lvl5 quickly, once your enemy saw damage of this skill at lvl 5, he can't come close to you alone (this skill should be maxed at lvl 8 or 9)

Move Quick: You need 1 lvl... no more until lvl 16

Toxic Shot: You need this but this is not scary for enemy. Blinding Dart please ;)

Noxious Trap (Mushroom): Most important thing after lvl 11. use mushrooms for escape and tactical attack when you are between lvl 6 and lvl 11.

You must buy Nashor's Tooth(%25 less cooldown!!!) and Rabadon's Deathcap...
(you never need Malady)
And if you buy more ap items or 2nd Rabadon, it is useless

Lastly, you can change Ad items...
but i think, crit chance is more important than life steal or health

use mushroom

in roads

...
and use them in grasses too :D
you are deadly, if you put mushrooms in roads (way of minions can't hit him: near death turrets)

Don't forget this: "you have %25 cooldown reduce" so you can put mushrooms faster...
(try to kill enemy who has oracle as soon as)