Suggest Treatment For Pain In Legs Followed By Weakness

DIFFICULTY STANDING AND WHEN IAM UP I HAVE TO HOLD ONTO AN OLD WALKER, CAN BECOME SHAKEY, NO BALANCE, CANNOT LIFT FEET FROM GROUND, WEAKNESS BILATERAL LEGS, ALSO STARTING IN ARMS, LOWER BACK PAIN,BUT MRI SAYS NO PROBLEMS,IT STARTED 2 YEARS AGO WITH SHOOTING PAINS IN LEFT LEG AND THEN THE RIGHT LEG,WHEN WALKING, AND ALSO LEGS WOULD SOMETIMES JUST FALL OFF CHAIR AND CAUSE PAIN TO START AGAIN, WEAKNESS FOLLOWED QUICKLY, AM USING WHEELCHAIR TO GET AROUND,CANNOT TURN OVER AT ALL IN BED.I AM 55 AND AVERAGE WEIGHT,WAS VERY ACTIVE PRIOR. THANKYOU FOR YOUR HELP.