Hello Doctor, I Have Pain In My Lower Back And

Hello Doctor,
I have pain in my lower back and some also in whole back. It feel very unhappy when i have back pain. I have this problem since last 2-3 month. i m a software consultant so i need to seat around 9 hrs daily. i consult with ortho and according to his checkup and X-ray i dont have any spine related major issue but there some muscle issue. i notice that when i seat for long time, the pain start. I also improved my posture and try to change the position after every 15 minutes. Doctor prescribe medicine that i took since last 8 day but its still not filling well. someday its not pain and some day it pain lower back and some time also pain and cramping in whole back. is this only muscle problem or something major? Should continue with some drugs? should i consult physiotherapist will be more better?