I got uncomfortably fat when my (now late-teens) kids were born. I decided to start running. I remember the first time out, failing to complete 2k across a bridge near where I lived.
I don't like being presented with evidence that I am incapable of something. It makes me angry. I can channel this into motivation.
I decided I was going to be a technical expert. I've read and taken advice wherever I can. I've now done marathons, stair running, cross country events. My "fast" pace is now 3m10s km.
My observations are two:
1. I have never "liked" the bit when you're getting ready to go out. The voice in my head keeps telling me to skip a day. I just zone out and ignore it. I've usually cheered up after about 5km.
2. Pain and injury are part of the deal. You will get used to this and come to accept it. Learning how to recover from setbacks will make you stronger.