You predicament reminds me of The Four Tendencies by Gretchen Rubin. The tendencies are based around whether you respond or don't respond to expectations, and whether the expectations are internal or external. From how you've described yourself, you sound like the common "obliger" type: responds well to external expectations, not so much to internal expectations. If that sounds like you, try finding ways to introduce external expectations for the things you'd like to do but don't. E.g., if you wanted to start working out, you'd be better off getting a trainer who expects you to show up than just telling yourself that you'll go to the gym.

It's not a scientific framework, but I think it's a helpful mental model all the same.