OUCH!!!!!!!!

I did a 10 mile run today to get ready for my half marathon next Sat. Why Why Why???? I ask myself. I knew i was not a runner before i signed up. I am in so much pain!!! I can't stand, sit or lay down and have rashes on the under side of my arm that sting like crazy. Any suggestions from any of runners out there would be helpful. What type of top to wear to prevent rashes and what to eat before a long run?