Running, healthy progression

I am an 18 year old high school student and I just recently (2 weeks ago) fell in love with the "sport.." of running/jogging.  Prior to my decision to run I lost 78lbs over the course of a year on diet (or lack there of) alone.  A lot of my weight loss was due to a stimulant I was using to help my concentration during my last two important years of high school.  I was using Concerta and Ritalin - which has Methylphenidate as the active ingredient and worked as an appetite suppressor as well.  Right now I sit at 201 lbs and stand at 6'6.  I'm a little underweight (as I have a large frame).  I have now been off the pills for a few months and am maintaining my current weight.  Two weeks ago I started running after work - 10:30pm, and started off at just over a Km.  Tonight I ran 5.5K.  My question to you is; What would be a healthy progression of distance, and is my current elevation of .5km - 1km, each run to excessive?  I'm really new to this and I would appreciate any feedback.

Thanks,
Chris - QuestionableMotive