running

my running days have become increasing diffucult and doubt is setting in before any real training has even begun. I have been consistently been runningon Tues, Thurs and Sat for this whole month, and I am starting to wonder if I am really going to be able to undertake this goal I have set myself up for.
I was able to laboriously complete 3 miles when I starting running at the end of Feb and now here we are at the end of March and I am only able to complete 5m. I ran about 6m one of the weeks but haven't been able to bring myself to that point again. It's frustrating since in my head I think I am doing all the right things and I obviously am not since it is not getting me any advancement. I know training doesn't officially start until June, but I want to complete the 10m run in May. As soon as I get up to about 3 m, my knees and feet start complaining. By the time I am done at about 4.5 or 5, my body is begging me to stop. I wonder if I need to incorporate the run/ walk method to train the legs to deal with the motion. Or maybe I need new shoes.
Next Sat is the Marathon 101 clinic. I'm going to ask some questions and hopefully receive the encouragement I am looking for to lift my spirits and work though this hump.