What is wrong with my body?

I noticed that in over 20 years of living, my body has stayed “too” consistent. No matter how much exercise I do, how much I stay dormant and indoors for months, how much I eat or don’t eat, my body just stays thin. I’ve always had a “lucky” body where no matter how much I eat and how junky the food got, I never gained weight. Everyone around me always told me that I was a huge eater and that I must workout or do some sports all the time to stay so slim, but in reality I just walk a few minutes to and back from school and play games the rest of the day. Still ate 3 times a day, eating the most during lunch and dinner. Never understood how people could get fat. From this, I knew it still wasn’t healthy so I decided to workout all parts of my body, 3-4 times per week and continued this for over a year. My gym friend also helped me with protein intake and what to eat, where the calories were roughly the same as what I was eating before. Did this consistently for the year, but my body literally never changed. I’m now a comic author and mostly stay at home all day, sat in my chair and literally do not move beyond going to the bathroom. I still eat quite a lot, but physically have not noticed any changes to my physique.

Some people may think I’m bragging, But this is really getting worrisome for me. I feel like something is wrong with my body and that one day everything is going to come back in some way. I wanted to ask what exactly this is and is it just how my body is built or if I have some sort of illness?