I haven't had a break for several years now. Due to some circumstances I take about 13 classes now. Most of them are important (QM, particles, ED, solid state, general (EM and waves), numerical methods), some of them not but still require work. And labs. I still manage to get As - somehow. But I gradually started to feel tired and overhelmed - I started to lose motivation and I don't have fun. I need to do many boring projects - they are not very challenging but it doesn't change the fact that they are really time-devouring. I feel like I waste my time. It seems that very important things aren't even mention in classes so self-study is the only way you can learn it and due to major switching my background is poor. I know that at undergraduate level in-depth self-study is a essence of physics. But it requires time and energy. I am simply too tired to do this. I can't concentrate properly and my efficiency is about 3%. Even if I get good grades my knowledge is still superficial. I am fully aware of fact that world of science is harsh. No matter how talented (whatever that mean) you are - success still depends on many external factors. So it's obvious that you must have at least great knowledge - it's a bare minimum that allows you to survive (especially in a challenging field). Yet I lack it. I wish I could rest properly and get rid of boring stuff and concentrate only on self-study in peaceful place at my own pace (ok it isn't very realistic - so at least have possibility and time to do sth on my own peacefully). I wish I could do sth more challenging (it may be possible but in next year) - challenging not in terms of amount of boring work. I think I could bear with this situation but like I mentioned before - I didn't have any break. I am just tired. I can't skip any class, choose them on my own or take a semester break. I think that this situation is quite normal in academia so maybe if I feel like this I am not fit to be scientist? In the end everything is a situation when you need to overcome your weaknesses. That's why I am asking for advice - what should I do in this situation?