Doc TRT here as well - I had the doc write me on her letterhead that I am on perscription testosterone and I require traveling with needles for my medication. That should cover ya... as far as the medication itself just make sure it has your RX script on it and pack it in your carry-on. Have it in a clear ziplock so you can take it out with the rest of your liquids that go sep' through the xray machine. Never ever had to be asked to show the script or the letter.. They see it as medication and aren't about to embarass you asking why you have needles and what medication you have to take.
Never been asked once going through Boston, Houston, LAX, NYC and I travel regularly internationally and domestic.