Too much of anything isn't good for you. Vitamin B-12 isn't a weight loss supplement; it merely gives you energy if you're too tired/fatigued to work out on a regular basis. It won't help you if you already have normal levels though. In other words, more isn't better.
There are risks with testosterone supplementation, such as cardiovascular problems like heart attack, stroke, and death from heart problems. Other issues caused by testosterone use include acne, disturbed breathing while sleeping, breast swelling or tenderness, or swelling in the ankles. You might also get high red blood cell counts that could increase the risk of clots. Some doctors believe that testosterone supplementation may increase the risk of prostate cancer... Always see your doctor before taking any supplement that contains testosterone or declares that it increases testosterone levels. For more information, check out the following link:
The best way to lose weight is to implement a healthful eating plan that consists of whole, unprocessed foods, including adequate protein and healthful fats and a moderate exercise plan.
You say you're taking testosterone -- the only legal way to do that is by doctor's prescription, so is that what you're doing? That part has me confused. If you're taking a supplement, say from GNC, that purports to increase testosterone, first, it might not actually do that, second it might not have in it what it says it does, and third, the amount of increased testosterone from supplements can help with energy but probably not do what you think it does -- and this is in addition to the above correctly noting that it isn't good for you. It also won't make you lose weight if your diet isn't a good diet for you. When you're really into muscle building, a high protein diet is essential, but a lot of ways of getting that diet means eating supplements that aren't necessarily good for you or for weight loss. The can build muscle, but overdoing protein is also potentially unhealthful. You don't really mention what it is that you're doing, but so far what you have mentioned is to build bigger muscles and give you more energy so you can work out longer, which doesn't necessarily mean you're doing that or that it will overcome other things going on with your health or your diet that are setting you back. Because you're aging, it will take more time to recover from layoffs than it did when you were younger -- it is what it is, and as a 65 year old male, I must tell you, it only gets worse. Be careful not to let vanity overcome sense -- I'm injured all over because I used exercise to overcome other issues and don't sleep well, and I'm all broken. You don't want to do that -- better to do it slowly and properly than overdo it. Respect aging. Relax with it, don't press. Find a diet that works for you, find an exercise routine that works for you, vary it -- blend cardio in with the weight training -- and alter it as you age as you need to. You'll get there without needing potentially unhealthful gimmicks. Now, where are you getting that testosterone? By the way, keep in mind that taking too much B12 regularly when your body is getting enough from your diet can lead to imbalances in your B6 and folate levels, which in turn can lead to a risk factor for heart disease. Be careful out there.