In short (op) you're normal. Testosterone raised your Dopamine level (neurotransmitter) giving you all the good feeling you experienced at the initiation of TRT. Dopamine, test and prolactin are all related and interact with each other. Once your body acclimated to the new, elevated levels it finds a new balance.
I'll add that there are things out there of interest in this area such as Selegiline which is an MAOB Inhibitor that helps dopamine levels:
Deprenyl (selegiline): the history o... [Acta Neurol Scand Suppl. 1983] - PubMed - NCBI
Read the above and do some further reading of Dr. Jozsef Knoll (sp?) who broke all new ground with it. Think life extension, etc.
Also research Cabergoline.