A bit confused

I'm 47 years old, 5'10, 250 lbs. About four years ago I was tested for low t. My total testosterone was about 300, and my doctor started me on Androgel. It worked a little bit; my total raised to around 400. I stayed on it for about a year, and my numbers held steady around 400. I stopped using Androgel when my insurance stopped paying for it two years ago.

Flash forward to a few days ago. I had been feeling down and weak for a while and went back to my doc to see about starting injections; since my insurance will pay for that. He did another test, and told me that my levels weren't likely to have gone up; so he went ahead and wrote me a prescription. I went to get it filled, and went back to have the nurse do the injection. Within a few hours I started feeling a little better; and now I have much more energy. I went back to the office today to pick up a copy of my blood work, but didn't see the doctor. My results from LabCorp showed a pre-injection testosterone serum level of 560.

I'm a bit confused as to why my levels went up that much on their own, and just as confused as to why the shot seemed to help so much. According to the results, my level was well within the normal range; and I shouldn't have needed the shot. It made me feel much better though; stronger, better mood, and it improved my almost none existent sexual desire.

I'll talk to my doc on my next appointment, but that isn't for a month. Any thoughts on my situation?