Picture this scenario. Two people talking about getting in shape. "I'm going to get in shape, think I'm going to go to the lake and swim a half mile."
The friend asks, "Have you ever swam before?"
"Well no, but how hard can it be?"
Can you picture the consequences of this scenario. Not pretty. Swimming is a skill. It needs to be learned, practiced and refined.
They run a few hard earned miles over the course of a few weeks or even months. Various things start to hurt, and they decide to give it up. "I guess I'm just not a runner."
Running is a skill, learn to look at it that way. Just because you can put one foot in front of another doesn't mean you know how to run. Just like you wouldn't dream of just jumping in the lake and giving it a go if you didn't know how to swim, get help with running.
Learn to look at running as a skill that is developed rather then something that is pushed through. Why do you think you see Elite runners doing drills before they run? Sure it's part of the warm up, but they are also breaking down running into individual components that can be worked on and refined. Instead of buying the most expensive running shoes, spend the rest to hire a local cross country or track coach for an hour a few times a month, to teach you some drills and tell you what to work on. It will save you some frustration, injury, and make it much more enjoyable.