If your mother was receiving regular pain medication at home, the same dosage needs to continue in hospital. It’s rare that a pain medication regimen is stopped altogether and given just "as needed" (what health care providers call “prn”).
One of two different things may be happening. Your mother may in fact be getting medications just as needed (prn), or she may be getting regular pain medication in a way you’re not aware of, and also getting additional doses as needed.
It’s important to ask the health care team to clarify which of these is happening. If your mother is in pain, ask the health care team about placing her on the dose she was using before being admitted, if that dosage in fact controlled her pain. If it didn’t, then her medication regimen needs to be reassessed.
If your mother is experiencing pain, you need to meet with the health care team to express your concern. You have a right to advocate for your mother if her pain is not being controlled.