So, with all the crap weather about at the moment I though I'd do some light running to maintain fitness and perhaps improve my cardio. I typically do about 12 to 20 miles on the MTB but have done very little running before. I got a gait analysis and bought the recommended trainers and on Tuesday 'ran' 3 miles. I spent 15 minutes stretching before going out. The first mile and a half was fine, I felt good and was enjoying it, however I felt my calves tightening and some lower back pain. I stopped and stretched some more and tried to continue but ended up walking the last half a mile. I stretched again when I got home and followed that with a hot bath. Since then I can barely walk and have had very bad lower back pain. Any ideas what I'm doing wrong and how to get rid of the pain?