Getting your blood work done and having your test levels checked isn't a bad idea, but I would be 99.99% sure that this isn't the issue. You probably weren't putting on much muscle mass because of a flawed diet and exercise program. Also, if you were fat, it can be hard to notice muscle gains. 45 mins per day of cardio 4-5 times a week sounds like a disaster for muscle mass in my opinion.
The hardest thing for me is that I wanted results, and I wanted them right there right then. It just doesn't work that way. This takes time, patience, and a lot of dedication. That's the bad news, the good news is that it is not difficult to do.
I literally have my friends asking me what juice I am on, the guys I work with come to me for exercise advice, and I look pretty darn ok, and this is coming from someone who was 265lbs in February.
Try the above program for 3 months. That sounds like a long time, but it isn't at all. 1/4 of a year invested to completely change your life is a small sacrifice. Take before pics, then take a pic once a week, keep them, dont show them to anyone, and watch your transformation. Record your weight and measurements once per week. These are all things that will keep you motivated.
Remember, you don't have to starve yourself. 2300-2500 cals a day is a lot of food, and you can still eat what you want in moderation. In the meantime, if you have the means to get your test levels checked do it. Nothing to lose by finding out
You can do this, and I wish you luck.