bionerd, muscle fatigue can be caused my multiple factors. first thing is,  you need ATP, so make sure you are eating properly. cup noodles give you tons of sodium and a part of your carbs but they are not what you are supposed to eat regularly. second, you need calcium, potassium, and sodium. well, looks like you've been getting a ton of sodium but you probably don't have much calcium and potassium in you. so, better way to get those boys would be to eat banana and milk. if you don't do any physical exercise, you better start doing some light exercises. you don't have to go to gym for that, you can do some light exercises at home. take adequate rest, recommended is 7-8 hours but who has that much time, right? but get as much sleep as you can. it's a good thing to take 20-30 min nap during the day if feasible. 
on more physiological aspect, your muscles might be suffocating (less oxygen) so, make sure you have good erythrocytes volume in your blood and make sure you are not suffering from anemia. if you don't want to go to doc, just drink a lot of fluids, and eat fruits; everything will get back to normal. 

now, i have a few suggestions for you: eat good food. i know you are a student like me and you are working your butt off to manage everything. but what will happen if you become seriously ill tomorrow? health is your frist priority. don't live on noodles and fast/junk food because they do more bad to you than good. cook at least once a week. i'm a guy and i still cook twice a week and i'm talking about daal bhaat tarkari, not mac n cheese. and don't count the calories, eat how much your body needs, burn off the rest. you CAN'T stay slim n sexy as well as healthy at the same time by not consuming food. the key is to eat whatever you need, absorb what your body needs, and burn the rest. but people tend to eat less which is terribly wrong and they don't even realize it, they are just happy thinking that they are fit and healthy. 

you are a woman which means you will be more severely affected by diseases than a male would. i'm not trying to discriminate between man and woman, just telling the truth. you are probably in your 20s and you might be thinking that you'll do just fine but guess what, today's noodle will hit you back when you are in your 40s. so, you better take care of yourself now. mari lanu kehi chhaina, jati dukha gare pani kura uhi ho so take some time to take care of yourself or you'll regret later. 

so, drink milk, and other fluids (fluid = jiuce, daal, etc, not coke n sprite ni!) eat good food, and at least one type of fruit a day. also, take multivitamins (those gummy bears like things). hope you'll take care of yourself and start feeling better.

- DrKanchho