In January My Husband Ha,the Flu. Ever Since He Seems

In January my husband ha,the flu. Ever since he seems like he,still has it. He had a flu shot . He took Tamiflu but since he has been very tired. No energy. Not eating well and is losing weight. When he does anything it causes shortness of breath. He's been to the doctor and has had blood work done. The only thing that showed was low iron. He is taking iron. With all of this going on he has a slight tear in a tendon in his left shoulder that is causing radiating pain to his front left chest. He is scheduled for more tests. However I am leaning towards walking pneumonia as I have had it before and his symptoms match that. The only difference is he does not have fever. Dr said his lungs seem clear but he is going to have a chest x ray done. Just wondering what this possibly be???