I've had lower back pain for months from bending over molds all day. Tried a new posture trick. Keep your feet wide when lifting heavy stuff. Engage your core too. It sounds basic but it works. My pain is much less now. I can work longer without hurting. Also do quick stretches during breaks. Focus on hamstrings and lower back. Takes two minutes. Makes a big difference. Give it a shot if you have similar issues.
Actually, a friend of mine messed up his shoulder from a similar repetitive motion. Tbh, he fixed it by switching which hand he used for lighter parts of the job.