Newbie weight lifter here looking for advice

Im 26 f weigh about 125 lbs and im 5'4". I've been getting into exercising for a while now but im still a beginner cuz there's alot i don't know still. My goal is gain muscle and get bigger. I started lifting weights about a week ago. I've been lifting dumb bells. My arms aren't that strong. I do 10lb biceps curls single arm. I've been doing 5 lb front raises and lateral raises 4 sets of 12 with them but my back starts hurting after a while. The pain isn't too bad but its there maybe like 4 outta 10(i also have lower back problems too- sciatica). Im wondering its because my arms are so weak that my back is substituting for the lifting and i end up working my back instead of my arms. Should i lift lighter weights?