I've gone 4/0 before level 3, and come back to level 5 mid laner and got stomped too. It's because kills are % based, and minions are flat, so 3 kills will basically never level you up, but minions will. Basically winning lane is the best strategy because you are rewarded and put ahead of someone directly. Also when you get an assist, the % experience is dived even further, so solo kills are the only real way to get ahead in terms of xp. If you are at 1% gained xp to next level, this is the best time to get a kill. If you are at 99% xp, this is the worst time to get a kill.
Also a solo kill is worth 300~ gold, but leveling up is worth 450~ gold in stats. This is just a side note to the fact 10~ minions are worth a kill, and so someone collecting a whole wave while you are gone is going to pass you with just that. Between xp and gold, the first 3 waves are worth almost 1300 gold.(About 4 kills worth of gold)