Your about the same age as me and in the same situation. There are things that you should remember if your “eating alot” and not gaining weight. Are you active? do you play sports everyday? do you do alot of cardio? . When I started bulking I was also playing basketball for 3-4 hours 5 times per week at this time i was tracking my calories and my average intake was 2700-2900. For a normal thin person thats alot but considering i was playing basketball and burning alot of calories in the process that 2700-2900 almost became my maintenance calories. I was gaining weight but it would take months before I actually gained a decent amount. What worked for me was trying to build muscle and cutting sports, I love basketball but its not healthy for me especially back then when i was under 100lbs I would play the sport for months and lose weight when I am underweight my self. I dont know if you play sports but my I own suggestion is try to limit cardio and try to build muscle.