This. Mike Mattesi approach about force is good aswell. One more thing, if it gets frustrating, stop. Take few A4 papers and just do few gestures without expectations. In whatever weird way or shape you can imagine as you get mental image. Allow your arm to flow, like quick sketching, bit faster and relaxed pencil movements. Again, ZERO EXPECTATIONS. Whatever you see on paper is ok as it is. Take 2-3 min per sketch then move on. Getting frustrated as you try to learn something is very counter productive and longer you stay in that mindset more it affects you. Learning isn't just what to focus on, it's also acknowledging distractions and slowly taking them out of picture. In your case is you getting frustrated due to not making progress as fast as you'd expect. And find different artists with different approach when drawing bodies and gestures. Take a bit from one and another bit from another and apply to your existing style. Just like what Bruce Lee did with his Jet Kune Do. In your case you can take few bits from Proko, few from Mattesi, other few from Brunet and so on. I don't know how many people use this method, but create a quick story in your head as you try to imagine male/female figure in different poses. Like if you try to draw figure laying on couch with her core twisted a bit and as one of her hands support her head. For example, she's posing to a photographer in a studio, room of X size, light coming from certain direction, couch being medium or large size,... etc.. Take that image and strip it down to blueprint layout, imagine space filled with lines. With practice you'll be able to do this super fast, i mean just a thought about a pose or landscape or animal or , or... and you'll have a story about it. You'll have mental image of what you are drawing. Later on this helps big time as you do imagination drawing. If your observation is good, you'll be able to draw literally anything you've seen many times, down to every detail and also change it in whatever way you desire. Think of it this way, you want to draw certain pose and all you can see with mind's eye are lines, which then connect into shape. Add value on shape and you get form. Put that form into perspective,.. and so on. That's construction. With story telling you help your mind with deconstruction part. Some people have easier time looking at whole picture and breaking it down rather than constructing it up from scratch. Life is yin and yang, art is too. But many people mostly learn about yin and forget about yang part, that's why it takes them so long and once they realize it, oh well, years go by. XD

You shouldn't look at it as problem, but rather as something you correct by practicing anatomy itself. You will get better little by little, but keep in mind, be fully immersed in it. Don't get distracted by external noise, focus. Also, problems create more problems and depending on your other beliefs it might slow down your process of learning. Learning process is psychological on many levels. And you're young, create some sort of plan in your head what to study and how often. Don't just randomly jump to drawing anatomy. And put more focus on parts you aren't good at yet. It forces you to go outside of comfort zone. Kinda sucks when you start, but eventually you'll enjoy it. Marc Brunet has awesome video on how to learn faster, "the secret rule to learn anything faster". He has very good points but don't take them word by word, go with what feels right to you and create new learning habits with information you already have and what he, or others, explain. If you wonder why some people learn super fast and others slow, it's about mindset, focus and goals.