It is true that herniated disks can cause muscle weakness. This should have been seen via the MRI. The MRI of the spine with contrast would not routinely show the hip, unless that was asked for.
If the MRI is normal, you may want to consider a more thorough GI evaluation. This would include a colonoscopy (which also would be a good idea given there is blood in the stool) and CT scan of the abdomen.
Regarding bone cancer - this is not a typical presentation. A bone scan would be the test to evaluate for this.
Followup with your personal physician is essential.
This answer is not intended as and does not substitute for medical advice - the information presented is for patient education only. Please see your personal physician for further evaluation of your individual case.
Thanks,
Kevin, M.D.