Such low levels are concerning at your age (well...at any age!).
Have you had your pituitary hormones checked? Low testosterone in the absence of anything else may be attributed to primary hypogonadism as a result of low stimulus from the pituitary (LH). Did you also have your progesterone levels checked?
Your test levels can be affected by stress, lack of sleep, over-training...
There's no point boosting your levels if your body isn't using the hormone.
I would suggest Gaspari's Novedex XT (clinically proven to assist in elevating test levels). This would be a good opportunity for a study - any suppliers want to get Simon on Some XT and then get some bloods re-done in the name of research?
Supplementing with DIM is also effective as well as controlling Oestrogen with products like I3C (indole-3-carbinol).
Failing that, you should see a hormone specialist. I see you're in Adelaide. (note to self - remove personal details from test results!)
If you want the details of a good hormone doc, drop me a PM.
Doc.