Left Hip pain

I have had a nagging pain in my left hip/left buttock for about a year now - it comes and goes but lately it is ocurring quite often. My doctor thinks it could be arthritis but I am not convinced. The pain feels like a deep soreness and sometimes it is a stabbing pain.  It happens frequently when I am standing or when I hold one position for prolonged times (such as sleeping).  It feels like a heavy pressure bearing down from atop my hip in a downward motion.  The pain is severe enough to where I cannot bend my leg to put my pants on; my husband has to help me put my shoes and socks on.  In addition, I have a lateral bulge about 1 1/2 inches long coming off the left side of my spine (about hip level).  The bulge feels like a tendon and is not painful when I press on it. The puzzling part is that while I am jogging or exercising nothing hurts.
I am a 45 year old female, I have multiple sclerosis but otherwise very healthy. I hate to blame all my aches and pains on MS but  - could it be?  Until now I have not had any problem stemming from my MS which I am currently treating with Avonex.  Any ideas what this pain could be?  Thanks