I was thinking about this while running on the treadmill tonight, and I think I have a plan.
I'm going to make up a schedule tonight, and I'm going to actively mark off time for the gym, for writing, and for practising the guitar. And I'm going to put it into Outlook, and set it to give me that annoying alarm thingy, so that I will actually be guilted into doing things when I say I'm going to do them. I'm going to start off fairly easy -- gym 3 times a week (which I'm supposed to be doing already, and which I do about 1/2 the time), writing twice a week, guitar maybe 3 times? That shouldn't be all that hard to do. And I know I'll feel so much better once I start doing all those things regularly again.
In fact, I feel better already, just having made the decision. It's going to seem terribly regimented at first, I'm sure. But it's all about making these things into a habit, so that it just seems normal to do them. Then I can start making up schedules for other things, like submitting stories... but let's not get ahead of ourselves.
Once I've got the schedule worked out, I'll try to remember to post it here, so that y'all can keep me honest.