What Causes Persistent Fatigue Even After The Fever Has Reduced?

I had what I thought was a cold last week and by Thursday night felt like I d be feeling pretty regular by Friday. Friday I did not feel particularly good, and at around 4pm, I felt oppressed by flu-like symptoms (aches, chills, fatigue). Got into bed as soon as I got home. Got up for a little while later then went back to bed. Since then, I ve been running a fever of around 99-100 generally at night (though today it s below 99), coughing/blowing out sputum, experiencing fatigue and constant ache in back of shoulders, and often dealing with shortness of breadth (about five minutes ago I breathed 29 breaths in a minute. Am wondering if I have the flu (contracted while getting over last week s bug) or pneumonia, and whether I need to get myself to the doctor. Sinuses and lungs have been clearing and gradually I feel lung congestion abating. (When I breathe right now, albeit shallowly, I feel no vibrating of mucus/murmur; it s like a normal breath in that respect, and the same has been true for a good part of the past two nights.) Also, fever is less today. Otherwise, still fatigued, spacy, etc..