Did your Scheuermann's result in kyphosis?  Possible spinal cord   compression? You have certainly set quite a goal  for yourself by   running, especially on concrete, though you are  somewhat safer from   traffic there. My hat's off to your docs if they  prescribed or condoned   this exercise for you, since your condition  presents postural  challenges  most runners do not face. These postural  issues are likely  to affect  the knees and ankles as you compensate for  spinal  inflexibility. I  suppose your body could take more than two  weeks to  get used to the  punishment.

I've  treated patients with  your condition and have  seen others with  similar posture, out jogging  or walking briskly, and I  can't help but  feel there comes a point in  life, when you must decide  whether to give  in to the condition, or to  fight back and suck the  orange of life  dry. Kudos to you for your  efforts, but I am hoping you  engaged in  some preparatory exercises and  conditioning before taking on  the 5k  challenge. If not, I really think  you should take a few month's  break  from your programme and work  on  some lower back strengthening,  rowing exercises, neck lifts, low  impact  trampoline work, and perhaps  some pool running to condition  your legs  in zero gravity. When my back  has been sore, I've even  parked at the  far end of store parking lots,  and run leaning on a  shopping cart - a  poor man's zero-gravity trainer -  and it makes you  feel like you are  running on the moon (if your health  insurance will  pay for it, there is  always the real thing that Paula Radcliffe used):

All  those mechanical issues aside, running outdoors this time of year  can  cause salt-loss through sweat, and one has to be careful not to   unbalance the electrolytes that are lost through sweat.  This highlights   another challenge of Scheuermann's, which poses the   possibility of  splanchnic nerve impingement that can affect the proper  operation of   your vital  organs. Persons with low adrenal function may  be more  vulnerable to  salt loss, as well as foot and ankle swelling.  This  effect would be  complicated by a low-salt diet, as well as by improper  levels of  potassium and B6.  Make sure all your electrolytes are up to snuff and  switch to sea salt. Swelling can be the body's attempt to  retain salt. A  thorough checkup  by your doctor that includes adrenal  and kidney  function would be a good  idea before you are cleared for  exercise in  warmer weather.