How can i get bigger?

hello everyone! im 16 male and i have been working out for the last 8 months so i could get bigger. i am only 58 kg and i want to build muscles. ever since i started working out (lifting weight attending Les Mills programmes like body pump) i noticed that my enduranced has increased but my weight is wither dropping or increasing and then dropping again rapidly. i have a lot more endurance and power that i had when i started. i can run for an hour without getting tired or lift 70 kg but i just look like a skinny person. also i am thinking of drinking protein shakes once every day after m done working out. mostly my diet does not include meat, nuts, eggs, fish and other food filled with proteins. i heard tho that protein shakes is supplement of every day diet. how often should i drink protein shakes and if i want to stop them because every glass is 3 euros and i may not be able to afford them how fast should i stop them? pls answer i need help!!