Sciatic pain after surgery

Im 34 years old and just had Microdiscectomy surgery last Thursday on the S-1/L5-1 lumbar region.  An MRI revealed 1 herniated disk that was pushed up on my Spinal Nerve and was causing severe pain in my right buttocks down to my right foot.  Well the doctor went in and found that the injury was probably there longer than what I said (1 month) because the disk was dried and stuck to the Spinal Nerve.  After surgery he said he was able to clear it up and gave me 8 weeks off work due to my job description.  I didnt have any Sciatic pain after the surgery and up until 2 days ago.  Now the pain feels worse and to the point that my Doctor didnt even do anything in the first place.  I called my Dr to see if I could get another MRI to see if the disk did herniate again. He told me they dont usually do another MRI to check.  So I guess what I need to know is why they wont do another MRI and how long does this Sciatic pain last and are there any meds that are better to deal with nerve pain?