Sorry if I appear a bit dense about the time line you're talking about. Are you saying that you've been producing breast milk for 17 years or is this something that has just recently happened?
And when you speak of your "monthly friend" coming early but was light for two days, is that also just recently?
As far as comparing your periods to your girlfriend, you really can't do that. We are all so different in our cycles and so many things can throw them out of whack. You can't set your clock by hers.
If your breasts are producing milk, or are secreting what you assume is milk, and your periods are changing, you really need to see your gynecologist to figure out what's going on. I doubt very much this is "all in your head." But I have no doubt you need to see your doctor.
Many women begin perimenopause in their late 30's and that may be what's happening with you, but only your doctor will be able to make that diagnosis with tests.
This is quite likely just your hormones beginning to gear up for menopause, but you can't be sure of that and you can't ignore what is happening.
Please see your doctor.
Peace
Greenlydia