Several things are probably the cause of this....
Your weapon and armor isn't good enough to attack the ppl you are trying to attack. You don't have an energy shield running....or it's not fully charged. The ppl you are fighting have better stats than you.
If by reading your posts that your stats are equal to your level then you should have no problem beating lvl 11-12's if your gear is top grade for your stats/lvl.
I am only a lvl 13, but take lvl 13,14,15,16's all the time, but then my stats are different than yours and not gonna say what they are
You need to figure out who you can beat easily and work from there, if that's started at lvl 7's and working your way up then so be it. You will find a comfort zone and be ok.