Don't get snarky if you haven't played every class to 50. Every class is over-leveled around 20-25, so that really has no bearing on the current conversation of being stuck at 45.
I, too, was stuck around 45 with my Knight, and it was VERY frustrating. I did most of the bonus lines and always did my space dailies, and had very good crafted armor/hilts, yet in the middle of Voss, I suddenly found myself getting pwned something awful.
I literally had to run around Voss, killing monsters for 6-7 hours to gain a level. I did this because I do not do flashpoints or warzones or those kind of things, because they are lame. Single-player all the way.
If this isn't an isolated thing, they really should address it. If you have armor and hilts and mods BETTER than what's being offered for quest rewards, and if you've done BONUS missions regularly, you should end up AHEAD of the curve, not behind it.