i doubt it's a slipped disc. if you can get up, walk around, and lift your filled laundry basket, it's probably not a slipped disc...
Slipped disc can usually be diagnosed from a description of the sudden onset of disabling pain, together with signs of sciatic nerve problems on clinical examination. It can be confirmed with MRI (magnetic resonance imaging) or CT (computed tomography) scans of the spine.
it sounds like you're lifting with your lower back, perhaps swinging the weights. a couple of suggestions:
1) get in your starting position for squats. knees slightly bent, back slightly arched and tight, and leaning forward slightly. this is good because it forces you to isolate the biceps to lift. you can't swing the weights when you're in this position. this does leave you open to bouncing with your legs, but try to resist that.
2) try leaning your back up against one of the padded backrests or up against a wall when doing biceps.
just give them a shot for a week or so. if it gets better, keep it up. if your pain doesn't go away in a couple of weeks, see a doc.