Low Sperm

My wife and I have been trying to get pregnant for almost two years now. She has pocs and a lot of health problems that come with that; however before we even got together she had a child and she has been to the doctor and they say she can have another since she already had one. Her age is in her late 20s. I am in my late 30s. I have never had my own biological child yet. I love my step son he is my son, but I would love to be around a child from birth as well as have something that is a part if myself and my wife. She is a very good women and I want to give her the world. I went to the doctor and they told me I have low T, with that I was given the shot I have been on it four over four months now and the doctor is rasing the amount needed since there has been no change (with getting pregnant and my sex drive). I do not know what to do I am almost at the point where I feel I am trying at to old of age to be a parent to a new born .maybe it's just not in the cards for us.