I'm Same age Ive been working out since I was 15 I'm getting ready to compete this September, I load creatine and it has helped me immensely to get stronger and add on muscle. I take carnivor beef protein after a workout it tastes like a hobos ass but it works well. I eat lots of lean meat and tuna to try and add weight, I weigh 74 kgs at the moment which is a 4 kg gain in 3 months since getting serious about my training. If your going to get a preworkout which I highly recommend get one of: bullnox, pre series bulk, c4 by cellucor or conquer unleashed. Get the most generic creatine monohydrate you can find. 1 kg should only cost 30$ anything more and it's not worth it. Eat tons of tuna it very low in fat. And if your looking for a fat burner try dexamine black or ephedrine but do as much research as possible it is dangerous.