Cold vs. Allergy

Good question, as it is sometimes hard to tell. I try to take few meds for either, having been around the block on that and come down to less is more, but your basic question still interests me.

If you have clear snot, treat as allergy.

You have to be aware of the symptoms to differentiate colds and allergy. That is the time for you to drink the medicines. The best way is still to consult the doctor.

If you're prone to allergies, you can usually figure out when they're happening as they tend to have triggers. E. g. if you're allergic to mold spores, it's likely that you'd feel more symptoms after a rain or a day or so afterwards.

Colds tend to also come with pain and fatigue that allergies generally don't have. Allergies tend to come with swelling that colds tend not to have. You mileage may vary, and these are general statements, but there are real differences. If you don't know, I would advise visiting a doctor, as what you think is allergies might not be, or might be treatable in some other fashion.