Questions about Pain pills prescribed by the doctor?

Ok heres the long story short,

I have been having bad lower back pain from an overworked/ pulled muscle in my lower back that is causing flare up in my sciatica. (this is not the first time) I went to the doctor. they checked everything, didn't take xrays but prescribed me Robaxin 500 mg (muscle relaxer) and Diclofenac 75mg (pain killer). Both are a generic of the originals. I was told to take the Robaxin 3 times daily for pain and the Diclofenac 2 times a day for pain. None of this is even beginning to touch this. My question is, is it ok to take more of the pain killer (diclofenac) than prescribed? Im only meaning like 1 more a day to make it 3 times a day instead of 2. Im not a pill head don't worry. Also, it has been 3 days on this medication, I space it out like they said and have only taken what the bottles prescribed. Should I go back and have them run Xrays? The pain is sharper now than it was, It just seems like nothing is working. Any help would be appreciated. Thanks!