I think I'm getting sick again

So I'm back from Poland, going to work- back to life as it's supposed to be :-)
However, I feel like I'm getting sick...
You know those times when all of a sudden, you have no energy, and you just want to sleep all day?
Well, this is how I'm feeling today.

I tried drinking raspberry tea with honey, added cardamon to my black tea, and took way too much vit C:-)
So far, I'm feeling the same, which is other words can be described as crappy! Excuse my language :-)

Don't know what it is about Brussels weather that just doesn't agree with me.
Can it be the humidity? Or the rain? Or everything combined?

Send me please some home-made remedies. I'm willing to try anything, as long as it doesn't involve going to the doctor:-)

Hugs