Track your caloric intake using the MyFitnessPal app or something of that nature. I literally have not eaten a food that I couldn't find its nutritional information on there.
Start at a daily goal of 3500 calories goal and go from there. Hit that goal on every training day (which is five days per week for me) and just eat until you're full on your rest days.
Do that for two weeks straight and see if you gain a pound or two. If not, bump up your caloric goal to 3800. Try that for a few weeks. Still nothing? Go to 4000 and above. Calories don't lie. It's simple, but too few people are disciplined about it.
As for training, make sure you're squatting and benching multiple times per week and deadlifting at least once if you so choose. Train them between 3-8 sets and between 2-15 reps. Write down every workout and increase a variable every week for each lift (so increase number of sets or reps or weight or a combination thereof).
And most importantly, be patient. Strength is a marathon, not a sprint; a journey, not a destination. And while you might want to gain 20 pounds of muscle and increase your lifts more than anything in the whole world, keep in mind that you still want to be training 10, 20, 30 years from now.
Let me know if this is helpful and how you progress.