I'm 170cm, 55kg and I just started working out at the gym about 3 weeks ago and I see some progress. I'm happy with it but I'm not too happy with my weight. Here are my problems why it's hard for me to gain weight:
1) High metabolism - Even if I eat a lot of food, I only gain few grams in weight for few hours and then it drops back(wtf)
2) Working - Don't have time to eat(Only lunch and dinner)

So I'm seeking an advice from you guys of what should I do to gain some weight and muscles. Should I buy supplements like mass or whey?

If important, here's my workout routine - chest, biceps, triceps, shoulders, jogging on treadmill for 2km in 15~ minutes

Yes its convenient to prepare store and consume. Also very convenient to get diabetes.

One big bag 10lbs only RM 300 but very less servings. One serving is like 2 huge scoops.

I used to drink hell lot of Milo from my previous office cause its free. Not much difference bro.

Any calories u put in can increase weight as long as you're eating more than you're using.

Your body is what you put in your mouth. If u want increase weight; eat more than u currently do. If you lose weight; eat lesser than what ur eating now. simple as that.