Not yet diagnosed, help me understand what is going on

Hello
I am 19 years old male and have some I can say serious issues with my muscles and no one knows what it is. It all started 2 years ago when I had a leg injury and was sent to a doctor for a ultrasound. Doc didn’t say a single word about my leg but was concerned about my muscles. He told me he thinks that my muscles are somehow weaker in his opinion, like they don’t get enough nutrition and I should see a neurologist. Just few weeks after that a started to feel weak while running or cycling. I used to run and cycle a lot, never had problems running for instance 5 miles or 50 miles on bike. Now I was struggling after just few miles on bike. My muscles were really tired and this happened again and again when I was cycling. So I decided to visit neuro, went to hospital for 2 weeks, got all blood tests done, head and spine MRI and EMG. Everything was normal (even CK levels) except EMG. It showed polyphasic potentials and a small myogenic lesion. I honestly don’t know what does it mean but the doctor told me it is nothing serious. So I was released with some stupid anxiety syndrome or something similar, but couple weeks later I started to twitch all over my body. Went back to hospital after some time and same results. Every blood test good, MRI good, same dirty EMG but this time I had a brisk reflexes. Was released with Benign fasciculatiobn syndrome. So I decided to reduce my physical activity and everything was going fine. But now I have noticed muscle wasting in my left thigh and my left shoulder. Part of my left deltoid is missing, a mucle of my thigh ( I believe the muscle is called vastus lateralis) is missing completely and have some other dents which are not on the other leg. While I still can do all the daily activities, can lift stuff and do things completely without issues I cannot workout much because my entire left side gets really tired and shaky. I cannot lift 5kg dumbbells 10 times with my left arm while I can do 20 lifts with right. Same with the left leg, it gets tired and really weak really quickly. Bike and running remains the same. I believe that I have some kind of MD because these symptoms refer to it but i am also afraid it could be ALS since I am twitching as well. Good to note I have been really skinny all of my life I am 5.7 ft and weigh only 8.2 stone (52kg) and I have been eating normally all of my life. Always struggled to put weight on.. Please help me understand what this could be. It has been 2 years since first symptoms and fortunately I can still jump, run (not much), do all the daily activities without problems but physical activities even small ones gets me tired to the point where a can barely move my muscles. Please help me understand what this is. Thanks in advance