Sounds like a seized caliper to me . One is braking harder than the other causing it to pull to one side . Get it on a flat car park with no camber and brake hard a few times with your hands off the steering wheel , if its seized it'll wobble the steering wheel .
Not that hard of a problem to fix , pop the piston outta the caliper , grease it and put it back in and grease the 2 sliders as well , should fix it .A good opportunity to get the pads , fluid and hoses on if your gonna grease inside the caliper .