Hello, 1. Periods due date can change due to many factors including stress, fatigue, hormonal changes, genital infection, etcetera. It is explaining why your periods were late. 2. Low-grade fever for the last three days might be a sign of virosis if you also are having problems with sneezing, coughing or muscle ache. 3. Being out late is an aggravating factor to your actual symptoms. I advise to: - Increase fluids intake especially water and tea - Take more rest - Take OTC pain-killers - Take vitamin C to improve immunity If no improvement or if the symptoms will get aggravated, then, should consult with your physician for further evaluations and treatment. 4. With regards to allergies, can you please explain what makes you think you might have allergies? Are your nose stiffed? Difficulty in breathing? Skin affections? Virosis or common cold symptoms would also give the clinical presentation for allergies. However, a deep clinical evaluation would give the difference between the allergies and any other common viral infection. Hope I have answered your query. Let me know if I can assist you further. Regards, Dr. Albana Sejdini