We also drink a lot of homemade Kefir. This is probably more important to overall proper immune system function, as 80% of your immune system starts or is otherwise dependent on what is going on in your GI tract.

Wash your hands frequently.

I'm with the crowd who thinks it may be allergies. It hits me about the same time every year (bow season) and lasts until frost. Ragweed is my problem. Antihistamines are useful now, but it was not until I underwent an extensive series of allergy shots that they were of much help. If it is allergies and not a cold, the supplements won't help much. Check with the doctor, as colds are just not a regularly "scheduled item". He can run tests and be certain. Good luck with it.

I left the teaching profession in 2012 after 20 years and have not been sick since.   Seems like I always had a cold of some sort from being around the kids (elementary physical education teacher).   Now I work in sales.   I try to not shake hands with people.  Contact with others is where it all starts.   Best remedy I have found is to wash your hands frequently.