Here's a suggestion I sincerely hope you listen to: Read the stickies here on this forum. They're loaded with a ton of foundational advice that will be instrumental in your understanding of the basics.
Asking GNC workers for help with regards to your diet is like me asking the Amish who solely use horse-and-buggy as a means of transportation to fix the motor in my car.
They're idiots.
I wasn't being a jackass in the above post when I said I know a lot of misinformed people who look fantastic.
I appreciate your comments about my body.
I also hope you listen to what I'm saying for future reference: Don't go around believing every guy that looks jacked. I followed that route in my early years and got nowhere. Most jacked guys are drug users who know next to nothing about anything relating to this stuff.
Here's a very simple lesson in energy balance as it pertains to your body.
Calories are energy. We either use said energy immediately to function or we store excess for later in various forms. One of the most obvious forms is fat. Fat is simply a storage depot for excess energy you consume. It does a lot more but no need to go into details.
When looking to gain weight, an obvious question you should ask yourself would be, "How much energy do I need to consume to lose and/or gain no weight... as in break-even or maintain myself?"
Once you answer that question, you have yourself a starting point.
Maintenance intake is a very individual thing and without being hooked up to fancy equipment, it's not something you can calculate precisely. Best bet is to estimate it.
Generally speaking, maintenance intake is roughly 14-16 calories per pound for those who exercise regularly. Your maintenance intake can be assumed to be someplace around 1800-2000 calories per day.
From here, with the goal of gaining as much muscle and as little fat as possible (that is your goal, right?), you need to institute a slight caloric surplus above and beyond your maintenance.
In all cases, the best bet is to try to minimize fat gains by eating/bulking smart. Yes, you need to eat over maintenance but given the fact that you can't fast forward muscle growth, there's no need to eat waaaaaaaay over maintenance. You want to find the sweet spot where you're seeing some weight gain, but not gaining too much fat.
Read that again. And again. And now again. Let it sink in.
An aggressive surplus would be 500 calories over maintenance to start. In your case, I'd probably shoot for 250 if I'm being honest. Be consistent and every 2 weeks evaluate your progress. If it's lacking, you know you need to ramp up calories. If it's too much, you know you need to back off a bit. Finding said sweet spot is a touch & feel process.
Another major issue here is how much weight did you lose? Have you always been really skinny?