Can short illness cause period delay such as pnemonia?,or stomach. Flu Hi my period is 4 days late,I have regular periods 28 days,but this month I had pneumonia prior to my period, I had a test but it is negative,I took cough syrup and some paracetamol,what coul be the reason,can I be pregant,I m still virgin but I have a bf,we just fooled around no sperm thank you