Everyday i count how many calories i eat, its always near 3400-3500. But for me its very hard to gain weight, i gotta have the fastest metabolism on earth. Before having acne i used to eat very poorly, lots of unhealthy fats, lots of simple carbs, yet i've always been skinny and ripped. I could eat everyday at mcdonals and dinner every night at burguer king and i would still have a 6-pack. It may sound good to some people, but it's a nightmare when you need to put on some weight and there's no way on earth.
Just make sure you are eating enough calories to gain weight, you dont want to spend money on a weight gainer and not backing it up by not eating enough natural foods too.
Read some articles on muscleandstrength.com there is loads related to beginners how struggle gaining weight.