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