Tight pelvic muscles. Deficient?

From the last one year I am having this problem of intermittent pain in my low back. Also I face the problem of frequent urination due to this.. Also bit constipated also. I have seen seen urologist ,orthopedicsTheir advice is I have muscle spasms which causes all this(CPPS). Need to relax my muscles. I have taken good amount Vitamin D , calcium , done bit of stretching exercise , but problem is still there,which is affecting my normal life. Based on some internet research, I feel lot of symptoms relate to Magnesium deficiency(muscle spasms, stress, consitpation) So my questions is,it possible to be magnesium deficient? and can it be the cause If yes , is there some general magnesium supplement , which I can try out.