Had flu-like virus week ago with low appetite,no fever.got period 7 days later and lighter.virus at fault possibly?

Not the virus: directly, but physiological or psychological stress can affect the hormones that regulate your menstrual cycle. Having an occasional late, early or different menstrual period is quite common. I notice that you say you have a low thyroid but I don't see that you're taking any thyroid replacement. Untreated thyroid disorders can also affect menstrual cycles. Dr. Anne