I've gone from being an exercise hater, to working out most days. Hated PE at school, hated gyms and working out in my 20s, didn't really do anything.
Then after my first child, I was carrying extra weight that I'd never had to worry about before. I started couch to 5k, with a goal of a Race for Life at the end of it. I also started seeing a PT, every fortnight for a couple of months, then monthly, he taught me about various exercises I could do myself, and weights, which I enjoyed so much more than the cardio stuff.
It still hadn't really kicked in, and then as I approached 40, I decided it was time to do it, I engaged another PT (who I still see 5 years later), and it finally clicked. Seeing the PT means that I learn tonnes of different things I can do at home as well, I learn form so I'm at less risk of injury, and I'm accountable - if I don't do anything between our sessions, I'm wasting my time and money, plus it makes the sessions even harder!
The other thing that keeps me motivated is my Apple Watch. I love the nudges it gives me to meet my daily goals, and although I've got no competitive spirit against other people, turns out I'm quite competitive with myself, so if my watch tells me I need to achieve something this month, I hate being defeated.
Your injuries make me wonder if your footwear and gait need looking at? DH for example needs to change his trainers really frequently - every 4-6 months, and has several pairs on rotation at once, otherwise he gets awful knees. I saw a physio a few years ago A’s was training for a 10k, and was getting knee and hip pain. She helped advise on footwear and supportive exercises which have helped immensely. I've suffered with plantar fasciitis, and I think my main culprit was tight calves. I had a couple of very painful deep tissue massages on my legs, and now try to massage my own calves most days which keeps it at bay.