I believe signs of low T can include loss of energy and appetite, as well as lowered libido. Signs of high T might include high blood pressure, heightened libido, increased appetite, and acne (could be more than usual, or the start of acne, if you haven't had it).
All that being said, I feel like your doctor made a drastic change in doses. If it were me, I would have tried biweekly shots on you, and if that wasn't working, I'd start adjusting dose. Going from every week to once a month seems like it'd really throw your body for a loop, and end up giving you really low 'lows' when you're in the last week or so of your shot cycle. You may want to discuss this with him, and keep track of how you feel as the month progresses.