Yeah!! You're doing awesome!! I'd be so excited if I were gaining at that rate
But I literally JUST started everything back up and I'm still ramping up on the maca. Hopefully I can get to gain 5 lbs every 2 weeks! Heck, just look at body builder websites, even they say that 3lbs a week is usually the max a heavy lifter & gainer can add without steroids, so you're doing amazing!!
I would definitely drink more water. The typical person needs 1/2 their body weight in ounces of water a day (so if you weigh 140lbs, you need 70 oz of water a day). Now, heavy lifters and people who exercise regularly need more than that, and people who take herbs need even more than that so they don't overload the liver. You weigh 64.7 kg, which is 142.6 lbs., which means if you WEREN'T exercising regularly or taking herbs, you'd need about 71 oz of water a day. That's just below what you're drinking now. 2 and a half liters is about 84 oz. So, you definitely need more water. Try bumping it up to 3 and a half to 4 liters a day. The easiest way to do this is to drink a liter and a half to two liters right before, during & right after your workouts, then one liter in the morning & one in the evening.
Another thing that will really help you is to up your protein intake! If you can't see yourself eating more hard boiled eggs or chicken, then get some whey protein isolate & just add it to your after workout shakes. You can also add it to milk at night too. It's just extra protein, and the whey isolate kind is the best I've used. Other kinds make me (and other people) bloat pretty bad! Also, make sure you eat a small meal of protein & carbs OR just a protein bar about 30 min before lifting, and a protein shake within 30 min after lifting. Eating 60% of your daily calories within 2 hours of lifting is ideal- it will give you sustained energy all day and really helps build muscle & gain weight since during that time, your body is a fat burning machine, we want it burning food instead of our fat & muscle
And now that you've been working out for a couple of weeks, do air squats on your non-lift days. Just do 5 sets of 15 reps of squats at home with no weights on the days you don't exercise.
When you do squats (at home and at the gym with weights, make sure to keep your core tight, so take a breath, squat down, lift up, then breathe out and repeat.) Explosive lifts are also best for gaining muscle. So, squat down nice and steady, dig that weight into your heels, stick your butt out and act like you're going to sit down, then quickly explode up and squeeze your butt at the top. What I do at the gym is stick one of those medicine balls behind me on the ground and when I dip down and stick my butt out, I barely touch that ball with my butt, then explode up.