I've played THREE PvP matches. And I'm having no troubling leveling, in fact since I hit Taris I've actually out levelled the content.
I've just got to Tatooine and I'm level 28...Tatooine is listed as levels 24-28.
I'm not sure what you've missed but you've certainly missed something.
Are you telling me you're not grouping with others for the heroics? Cause if so just give up now, you'll struggle the rest of the game.