I hit a similar wall on my energy/energy blaster around lvl 20 as well. Are you playing primarily solo, or on teams? In a solo situation, the best advice I can offer is try to 1on1 as much as possible. If there is a large group, snipe the guy closest to you and drop him asap. Sometimes dropping one baddie in the mob before you get hit makes all the difference. Second, don't be afraid to run. when your health hits half, look for an exit strategy. My blaster turned the corner at about lvl 30 and is one of my favorite toons now, so don't give up.
If you're teaming, be careful of aoe attacks as they can pull aggro away from the melee characters who are designed to take hits. Try targeting through the lead tank, that can help limit the amount of aggro you are taking.
I've played and enjoyed my blaster for 18 levels, having little to no trouble.
Then I hit level 18, gained my first hold, and started dying like a fly. My difficulty settings have been untouched, that being I fight enemies at my level with the equivalent of 1 hero.
I don't even have bosses set to show up when I'm alone! And really it doesn't matter because I've been dropping to minions. Just minions, nothing special, just regular groups of minions tend to kill or cripple me.
Am I doing something wrong? I'm playing like I always have on this guy. Do I have to follow specific ways to start a fight, do I need to stick with groups for a while, do I need to lower the difficulty level (I really don't want to do that unless I have to), or do I just suck?