I've been going to the gym since a month. I'm 20 years old. I'm about 180 cm and about 70 kgs. My posture is bad and I have a large butt. I'm very insecure about this actually and I want a lean physique bad, like real bad.

My question is this though: when will the starter gains kick in? My ltr told me that I've grown some chest muscle but when I look in the mirror I dont see it quite. I still feel like my butt is big, my posture looks like a bent giraffe when I'm not controlling it and when I control it, I seem like I'm tensed out. When will it get better? What should I do more? I'm going to the gym 3 times a week. I try to eat the best I can. I hope I can get some advice on what to focus on and when will the transformation actually begin?