suddenly cant run

Question
I recently finished my first half marathon, (which was absolutely great!)but now find that I am unable to run.  I took a couple of days off after the half and then set out for a usual run and felt like I had never run a day in my life.  I felt completely out of shape, even getting side cramps!  I have tried again numerous times, but this is how every run has been.  I had planned on signing up for my first marathon and was really excited about it but now don't know if I can do it.  Can you please help me understand what has happened and how to fix it?

Answer
Hi Carrie
Congratulations to you,great job.I would like to answer you question properly with the necessary information to get you up and running with without further damage and extend your great experience,but i would first need a complete bio of your past and present training for this race,how long you trained and specific runs,distances and how long you have been running to date, plus your height weight age,and what your post specific area's of problems of discomfort and the date of the marathon you intend to run.Get me this info Carrie and then i will take a good look and get back to you.

All the very best

John