exercise to strenghten core muscles

I have had major back pain for months.  I literally couldn't get out of bed and was in constant pain for no apparent reason..

I am a 65 yr old woman 4'4 and used to lift weights in order to not injure myself lifting heavy objects.  I lifted #50 plus items (required for my work)   After an MRI and two steroid injections into the base of my spine, I am a little better but still suffer with constant pain.  The physiatrist said I should do exercise to strenthen my core muscles and lift weights but not to excess and he thought 50 lbs was execive for my height/weight.   He disappeared without telling me what kind of exercise I should do to strengthen the core muscles and wants to see me in 2 months.  I don't want to wait 2 months for further advice from him.,
  

I have free weights, a bowflex, stationery bike as well as a street bike and a nordik track.  I desperately want to do whatever it takes to strenthen my core but am terrified of injuring myself and be back into not being able to get out of bed.   There is a lot of conflicting information on exercises for your back.  

[gymdandee]

http://www.menshealth.com/fitness/plank-walkup-pushup?cm_mmc=EOWNL-_-05112011-_-html-_-image

[gymdandee]

http://www.livestrong.com/article/18490-abdominal-exercises-not-hurt-back/

[sorryeyes]

Thanks for the links.  I am actually a woman who is 5"4 not 4'4 big difference and as yuou can tell a lousy typist.:)  

[gymdandee]

And I thought you were a Dwarf! :>)