Lower back pain

Lately, after lifting heavy bench or bicep exercises, my lower back tightens up and is painful for days. Is the cause too much weight? Poor technique? or both?

I am wondering if arching my back during bench exercises is the cause. Should I concentrate on keeping spine straight during all exercises?

Thanks for all of your help!

Yes this could be the cause especially if your butt is coming off of the bench. Your lower erectors are probably being used to lift the weight as well as when you curl. Try sucking in your stomach and tightening as this will keep the resistance (even when standing doing curls) to your core vs. all the strain on your back. I can guarantee that you may be swinging or leaning to one side when you curl back and forth if you are alternating. try lowering the weight and focus more on the contraction of the muscles vs pushing or curling the weight up.