Hi Dana, I'm new here too. Several things come to mind. You obviously have the desire so that's a good start. First have your bike seat adjusted and make sure you "fit" your bike so you will be as comfortable as possible. I think that having fun is crucial to motivation (motivation is a fickle friend; it come and it goes, so don't rely on that to keep you going). I am a "destination" rider, so for example, I'll ride a couple of miles to a coffee shop then stop and enjoy a drink; or maybe to the library that's 2 miles away and check out a good book, etc. So I know that I get a "reward" when I get there. Eventually I ride to places that are farther away. I take my time and ride however I feel. If I feel like going fast I go fast. If I feel like going slowly and looking at the flowers in everyone's yards, I'll do that. The point is, in the beginning to make it fun. As you said you're not training for some big event. That's not to say that you won't eventually train for something, but right now you're trying to get back into the saddle (literally). Be loving and gentle to yourself and give yourself positive affirmations for a job well done (I doubt you'd be so hard on a friend who is in your same shoes). You are building yourself back up and Rome wasn't built in a day. Build on your strength/endurance day after day, week after week and you will get there.
Happy Riding.