How do you know if you're asking too often?

Something I keep circling. My partner is completely fine with this and always has been. She has never once made me feel awkward about it and she offers as often as I ask.

Despite that, I have started keeping a rough count in my head, and I get twitchy if I think I have brought it up more than once a fortnight. Then I go a bit quiet about it for a while, which she has noticed and asked about, and I did not have a good answer.

Is there an actual measure for this, or is the counting itself the problem? I would rather sort out my own head than keep doing this slightly odd rationing thing.