I'm 20 years old, 5'7 and around 120lb. I want to gain some muscle and it's been 3 months since I started hitting the gym. I started with some beginners program from the internet but now I'm looking for something better. I'm thinking about SL or Greyskull but I have zero knowledge about fitness so I can't decide what program is the best for me in order to gain size.

I believe I have my nutrition on point - eating a lot of carbs and 2500-2600 calories a day (may not sound like a lot but it's 500+ more than I used to eat)

Also any tips about gaining weight will be useful.