That's weird I find healing to be the easiest and had no trouble with my sage but I think it's just not something you're used to. Make sure to use stuns, interrupts, remember that your barrier abilities can be applied to your companion, heal only when needed and use your lightsaber to attack and get your force points back up, get good gear for your companion (including an endurance +41 crystal) and make sure to send him in first so the enemies attack him and not you (don't want to be panic healing yourself over and over and lose all force points only to die). If all else fails, you can always ask other players for help on a particularly hard enemy.