Soraka question- need help

I have been playing Soraka for a while. Since the nerf a while back, I have had problems with my level falling behind after around level 7-10. I am not sure what is going on. Should I kill some minions or what the deal is, but how do I keep my level the same as those getting kills? Someone suggested I do more of an AP build than what I am using (armor and magic resist + AP runes). Only 3 points in sorcery in masteries. Help!