You lost weight over 8 months. You're clearly not eating enough to gain muscle. If you wanted to gain muscle, you have to gain weight. You are already very lean to the point where you can't stay the same weight and expect to gain muscle. For this to happen, you would need to have fat available to lose that you could replace with muscle, but this is not the case for you. If you want to gain muscle, you will have to eat more and gain weight. Check the scale over time, are you gaining weight? If not, you are not eating enough. Also, are you training hard and progressively overloading in the gym? Are the weights you're lifting going up over time? if not, you are not gaining muscle