Usual disclaimer here – I'm a medical student and not yet a doctor – thus take what I say on merit and not as authoritative. That said I am interested in the endocrine, autocrine, and paracrine systems, and have just completed a module of study about the human female endocrine system.
Unfortunately think many clinicians are not fully familiar with Trans hormones and thus may needlessly worry about high prolactin levels which, unless I have not understood things, are actually a fairly predictable consequence of the slightly backwards way that HRT drives your levels, and not actually a huge cause for concern.
Normally there would be a complex interaction between pulsatile GNRH, FSH, LH, PRL, Progesterone and Estrogen. All of these hormones exist and act in cyclical dynamic balance with each other – where changes in one, trigger rises or falls in the next.
There are complex feedback regulatory mechanisms involving the pituitary and Hypothalamus, but because you drive your levels with artificial inputs, and at a level beyond bio norms you will get some anomalous levels with things like prolactin and it's not a cause to worry as long as the patient is otherwise well.
Returning to the original question about lactation – this is normally triggered by sharp falls in estrogen and progesterone levels after pregnancy. So if you are lactating it probably suggests that your levels are not being maintained properly and either fluctuating more widely than ideal, or are generally rather low.
