Question about herniated disk

About 7 or 8 years ago or so I had an MRI that showed a herniated disk in my lower back.  I have had lower back pain but not much else.  I started college in August of 2007 and started carrying a backpack that is probably about 10 - 15 pounds.  I walk up 3 flights of stair 3 days a week.  I am 35 yrs old and here is my question.  At the end of November of 2007 I started feeling a pulling in my calf in my right leg and it eventually started in my left leg as well.  Can a herniated disk cause your calf muscle to feel pulled and to cause pain throughout the calf???  My dr seems stumped.  Blood work is fine and my back x-rays showed the changes in the lower back as described above.  I can feel a little tingling in my right foot as well and sometimes feels like there is a pinching behind my knee.  The pulling only seems to happen after I get out of bed in the morning or after I have been sitting for awhile then get up to walk.   Does that sound like anything more serious than just a disk problem?? Do you think the weight of my backpack is causing me problems??  Any help would be great.  Thank you.