I wouldn't start TRT if I were you. You have midlevel testosterone levels. And unless you use hCG your sperm count will go down.

How long are your weight lifting sessions? How many sets per bodypart? I find that as a 40yr it is easy to overdo the gym. Your joints can't handle as much stress as when you were 18. 3 hours on basketball can take its toll. Sometimes less is more. Glucosamine with MSM can also help your joints.

Also you definitely are not going to lose your belly fat while taking a weight gainer. It's pretty much one or the other.