The post above has told you the answer to your question but I thought I would let you know your options and concentrate of a few other aspects of the problem just fyi....
Things like Alpha Male effective but again for only as long as you take them: you're young and already have T issues so I'd firstly recommend looking at making the most of what you have;
I am sure you have looked at this hard already but for now try and change around with the other factors in your life. As a personal trainer you understand the effect diet, exercise, stress and rest can have. Try and maximise the benefits to be gained form these, cut back (where you can) on the endurance work any way you can and get ample rest (though I understand about the early mornings etc) generally try and identify the stress factors and reduce them.
You would be amazed what these changes can do for symptoms connected to low T.
Also if it was me, I'd get a second opinion, doctors are just humans with their own views and prejudices. In your like of work health is all the more important, get tests done to ascertain why your T level is so low. If it were me I'd get them to do a full blood work to check related hormone levels you can also get them to check your hypothalamus and pituitary for abnormalities. Be assertive if you have to, tell them what checks you want and get them to give you the results so you have a record of the facts - not just their opinion on the facts. If your T is borderline low then that may be enough for another doctor - especially at 24
realise that T therapy, if you are given it, is a ball and chain (albeit a sometimes welcome one) - a lifetime commitment and one that may not be covered by insurance etc so (as you say) you should look at all the other options unless it is really neded.
There are two ways you can go non prescription or prescription : it's controversial but arimidex taken a couple of times a week has been shown to boost T by as much as 40%. again that you would take two times a week from now until the year dot and your doctor will take convincing.
Best of luck mate. Let us know how it goes.