calf pain,muscle atrophy related to ALS

I,m a 39 years old woman and about 3months ago,I,ve started to have this strange pain in my left leg,inferior to my knee,the pain changes very much,sometimes dull,sometimes sharp and aching,sometimes burning sensation.after 1 month,my knee started to show problems too and my dc said i had chondromalacia patella but it is a result of the weakness of my leg,and today after many sessions of physical therapy,my knee and leg still hurts ,i cant walk for longer than 10 minutes.so far my blood tests ,MRI,bone scan,EMG,have shown nothing,and to top it all  my calf,s muscle has shown signs of atrophy...can any one think of some way to find whats wrong with me ?could my symptoms be the early stage of ALS?