Since you've read Percy Jackson, I assume that in spite of your age you're not too cool to read those "kids' series" which can and are easily enjoyed by adults as well.
So...
JK Rowling - Harry Potter
Derek Landy - Skulduggery Pleasant
Jonathan Stroud - the Bartimaeus sequence
Diane Duane - Young Wizards
There is also a whole lot of urban fantasy out there that might qualify (in addition to the Dresden Files mentioned above) - just browse any urban fantasy categories in any bookshops and discard those that
focus on vampires and werewolves (although those often have witches and magic as well). One that I'd recommend is the Rivers of London series by Ben Aaronovitch.