I am also new in this running thing (starting the C25K tonight after work), but from what I have read - shoes are key.

Could you need new supportive inserts for your sneakers?  Were they purchased specifically for running?  I know that years ago, when I tried to start running, I used my beat up old Nikes and my ankles paid for it.  This time, I actually went out and got running shoes and some inserts that were a little firmer than what had been originally used in the sneakers.  They are more shock-absorbant too, which is important for me and my weight.

Just my two cents.  I'm certain that other people on here will have more insight..  In the meantime, congrats on week two!!!  =)