There is no such thing as overeating. There is only under-exercising.
Some of the best advice I've heard for people who have trouble gaining muscle is this:
Going to the gym and working out hard is important, but what really matters is that you eat a shit-ton of food. Every time you sit down to a meal, eat until you want to cry, then eat some more.
And if you're following that diet plan and you're making every workout better than the last workout in some capacity with either 5 more pounds or 1 more rep on a lift, then you'll gain weight. Depending on what kind of muscle fiber ratios and what kind of genetics you have, you might need to become absurdly stronger than you are now in order to see sizeable gains. What's your barbell row 6RM? Double that number and you've gained at least 20 pounds.