I am definitely the same way and I know first hand about how it's difficult to get back into it. While I do use charity rides or other rides to give myself a timeline, I also know I am very bad at long-range planning. Part of me doesn't see the result of exercise as a long and slow process and I then think "I can do it tomorrow".

My two tricks are:

I tell myself I'm going out for a certain short distance and if, at that distance I am not having fun, I'll turn around and go home. I generally go farther because once I'm on, I love it. Periodically I do the minimum and that's ok...I didn't fail because that WAS the minimum.

I also just got a heart rate monitor. For somebody bad at long-range things, this toy is cool! I can see immediately calories burned, max heart rate and a myriad of other things. Yesterday I went out for a run (running is not my strong suit) and as I watched the calories burned thing go higher and higher, I ended up going an extra mile because it was pretty impressive just how little exercise it takes to burn calories! (Yes, I know it might not be 100% accurate but still, it makes me motivated and gives me different goals!)

I also agree with others about making it fun and using the bike for errands. I think we get so locked into thinking what a ride means that we forget we can be on our bikes and not have it be "exercise"!

Good luck. It has to be so rough coming off an injury and being away from work for so long.