I use sambucol when I catch a virus.  Love the stuff.  I also drink the effervescent tablets as a drink.  The tablets are lower dose, so more of a preventative than a treatment.
 Is there any reason why your immune system may be compromised at the moment?  I know there are many reasons that this could be.  When I started working in a university I caught every bug going.  All the students used to bring them in and spread them round til no one was bug free for months at a time.  And I understand it, the same thing happens to teachers, or people who work shops...
Might be worth discussing it with your doctor, if you haven't got a reason like that for catching so many bugs.
Having said that, raised blood glucose also compromises the immune system.  Do you self-test?  And if so, what range does your blood glucose run at?  If you are running high, then adjusting diet or meds may bring things back into line...?
Hope that helps.