What should I be doing?

Let me share with you something that's given me a bit of anxiety while I've been travelling (and it's something that gives me a bit of anxiety in daily life as well; it is magnified by the fact that I'm travelling). It's a thought, that can be phrased as a question, that can be repeated over and over, in the background of what you're doing: How can I best be spending my time right now?
As I mentioned in my "to-do" list, I'm hung up about the fact that I'm not able to write anything. I feel like I'm getting too old to keep saying that it's something I can do a little later. If I wanna have some artistic masterpieces to my name (and I do), I'm going to have to be productive. I'm going to have to write. I don't know from where stems the source of this absolutely paralyzing anxiety on the matter, but it's there, and it's been there for a long, long time now.
So anyway, that thought keeps coming up: How can I best be spending my time? I sometimes feel wasteful if I spend too long in a museum, wake up too late in the morning, turn in too early for the evening, wander too aimlessly in a new city. I just get the feeling that whatever I'm doing, I should be doing something else.
Now, this is, of course, not a rational thought; it's an anxiety. Rationally, I understand that this is a self-defeating anxiety, since I'd be enjoying my time if I could just let it go, but since I can't let it go, I'm not enjoying my time as much. And of course there are times when it goes away. These are typically times that I'm spending with other people; people I like. So what I'm then asking myself is, do I need other people to enjoy myself? Is this why I'm so miserable in those places and times where I feel like I can't find anyone, or when I see people I want to talk to, and just don't?
I relate this to a deeper insecurity I have about needing the approval of other people to feel validated myself.

Man, I just spilled something heavy on you there. Sorry about that. Just thinking and typing...