Hi thanks for asking question. As you have difficult breathing your case should be concerned. Here are few possibility. 1.First as you had history of viral flu you might have viral respiratory infection like rhinitis , sore throat or bronchitis.complete blood examination may reveal lymphocytosis.Chest x ray also helpful. 2.Second if fever and cough associated then pneumonitis like cause has to be though and chest x ray done for it.If cough productive and bacterial infection is under suspicion then antibiotic needed. 3.Third you might muscular pain as a part of respiratory infection or by muscular strain. Pulmonary function test useful in differentiating restrictive or obstructive condition. 4.If you have hypertension or diabetic then after ruling out respi.cause still if diagnosis not clear electrocardiogram useful for ruling out cardiac causes. I hope my suggestion will helpful to you. Wish you good health.