I read this as your doc's an idiot and is going to hurt you. If he's actually injecting you with 400 mgs every two week he's clueless as to how hormones work. He's injecting you at the terminal life of test, not it's half life. I f'n hate docs that prescribe meds that they have no clue about. Drives me nuts. Look at this chart which shows what happens after an injection or a normal dose of test:
Now, your idiot doc is injecting you with excess test in hopes of making it last longer. Not considering the massive spike in estrogen it will cause after injection. And you say you're prone to gyno? I hope he also has written you for adex at least. Ok, enough of my rant. Find a new doctor asap.
When it comes to cycling if you are just getting back in the gym it's the last thing you need to do. Spend some time and get yourself back in decent shape and then consider it.
Oh, and welcome to the forum.