Hi Ellie
Sorry you are having a tough time. I don't know much about hyperprolactinaemia but I have been in your shoes, being told I'm not ovulating. In my case it was PCOS (a year later however I am pregnant, so things can turn around and hopefully they will for you).
Just wanted to say, firstly, about the gonadatrophins - by this do you mean FSH and LH? I'm not sure what you mean by 'low' because it is normal - and a good sign - for these to be low at the beginning of the cycle. FSH ideally should be under 6, and LH should be about the same at that time. Sorry if I'm barking up the wrong tree here, but just wanted to reassure you about that.
The low progesterone on day 21 (it should actually be taken 7 days before your period, so hopefully it was timed right) simply indicates that you didn't ovulate that month, but it doesn't tell you anything about WHY you didn't ovulate, which is what you want to get to the bottom of.
Secondly, while I don't know much about 'normal' prolactin levels or the drug you mention, I would think that if you are still leaking milk, it is quite possible that there is enough prolactin in your system to suppress ovulation, and would therefore push to investigate/treat this further as the first port of call. I would explicitly ask your Endocrinologist about that. Prolactin is known to suppress ovulation.
If that's definitely not the case, you should be sure to have all the other hormone tests - testosterone (to check for PCOS) and thyroid, as well as an ultrasound of your ovaries. And Helen is right that you should be referred sooner rather than later.
Wish you lots of luck kick starting your cycle again.