Bottom bracket skrew keeps coming loose

My left crank arm screw keeps coming loose, screw locking fluid doesnt help. I'm avare this is probably because my bottom bracket got worn out, but I've only been using it for about half a year after I switched from my previous one that came with the bike for the same reason. They're square tapperer bbs so they're quite cheap, but no one else I know who uses them has had this problem, so I'm confused on why it's happening to me. Has anyone else had the same issue and what did you do to solve it ? My current solution of tying an allan wrench to the screw and crank arm seems suboptimal...