Bernadette,
You did not say where your cancer is.... The reason your Oncologist wants to do blood work and scans every six months is for your protection. The scans will pick up any cancer if your cancer returns.
No, 'pain meds' are not prescribed based on results of scans.
I would suggest you listen to your Oncologist.
Keep a positive attitude, have hope and faith for many years to come! ;)
Prayers and blessings,
B