If you pull out the fire control group (large pin at the lower rear of the receiver), you can likely see what's happening. Maybe the hammer isn't resetting properly, maybe the mainspring is broken. The function of the BPS is pretty simple, so once you get a birdseye view of the trigger group it should be easy to see what's wrong, and it's pretty straight forward to pull it out to take a peek.

If you're not comfortable pulling that off, then time to see a gunsmith.