When you say BB, presumably you mean the bearing cups screwed into the bottom of the frame? They are handed, with one being a reverse thread, the idea being that they should self-tighten. However they shouldn't be loose in the first place and the longer you allow this to go on, the more the threads will wear and the more sloppy the fit will become and the more difficult to fix.
Get them sorted though. If nothing else, tighten them in with a gentle grade of threadlock. I can't advise but there must be a special assembly compound for this job. If you continue riding with them loose you risk damaging the frame irrevocably; they will self-tighten but not to the same torque as they need to be properly fitted.
Had something similar on a cheap BSO i was doing for someone. BB was loose, so adjusted it up...only for it to come loose again in a day
BB shell was cream crackered. ( at that point we agreed it was a write off, so i suggested welding the cup and cone type BB in place...that didnt work very well either)