Unusual Leg Pain - MD advice needed

Hello.  I am looking for some insight regarding the leg pain that I have had for the last 2 months.  I have severe, constant pain in my left leg, essentially along the lateral and posterior aspect near the knee, which feels like a deep, cold pain (not really burning).  It does not shoot down the leg, but seems to just come from that area.  It is about an 8 out of 10 all the time and worse with certain motions (ie. when I push my toes down on the floor, sometimes with climbing stairs or movement, or crossing the leg).  There really is no pain in the back, lower leg, hip, thigh, hamstring, or ankle.  I do not know what brought the pain on; there was no injury or trauma.  The leg also feels somewhat weak.  I sometimes lift it with my hands when I’m either getting into or out of my vehicle (but some of this may just so I avoid the pain).  There is no pain with massage or pressing the area, and it really does feel deeper than muscular pain.  I assume if there had been a ligament or tendon injury I would have known that?

Of note, I do weigh about 20 lbs heavier than my normal weight, as I am 8 months post partum, nursing, and still have that 20 lbs to drop (eventually).  I am not interested in taking any medicine for this problem, especially since I’m breastfeeding exclusively.  

As far as other health problems, I have coccydynia since 2003, which I have just dealt with (my coccyx is at a very bad angle, like chronically) so I have had a couple of steroid injections to the joint there.  I also have postpartum hypothyroidism and had gestational diabetes, but other than that, healthy.  Fhx of RA in my mother.  No history of neurologic diseases.  Daily meds are prenatal vitamins and Levoyxl 25mcg.  

I saw my PCP who was kind of stumped.  She didn’t really know whether to send me to ortho or neuro.  We are basically looking for even a differential at this point! Should I be worried about systemic illness given that it’s been going on 2 months or is this likely damage to one nerve? (however, how does one nerve get damaged without trauma?)  Recommended studies, etc. would be very helpful…

Thank you so much!