Extreme tiredness after a viral infection

Just getting over a virus.  Started with a sore throat, then a bad cough.   This was 10 days or so ago.    Cough is almost better and not keeping me awake like it did, but am feeling so tired and weak.   How long shall I give this exhaustion to stop ?  Am due for blood test soon, but this is only for my calcium levels.   I am taking a tonic now (Metatone) and hope this would help me.   I am 75 years of age

It can take up to several weeks, don't worry.

You could be describing what I have had, I cannot get past lunchtime without my knees knocking, and trouble standing up, all post viral nasty headcold type virus, am taking vit c and multi's, they do seem to be helping, a little, but its just a matter of taking it easy for a couple of weeks until I shake it completely I think.  I suspect you are the same, just take it easy for a couple of weeks, rest when you need too rather than push through if you can.

How many weeks can it take?