Hai your father need to consult an ortho doctor first .
And be sure that he shouldn't prescribe medicines for himself. If a person has some other underlying issue, these painkillers will only subside those symptoms for time being.
For timebeing he can go some gentle stretching and strengthening exercises. And hot pack application. If you can dip a cloth in hot water and then place it on his painful area that will help him relax his muscles
Next Steps
Let him get done a full body check up. some people may develop pain due to
vitamin deficiency or may be due to his age or may be due to his daily activity, sitting or sleeping position.
Health Tips
Best is to meet an Orthopaedic doctor first