See below. Sometimes, it's hard to tell the difference! if there's a fever, it's not allergies. Itchy nose or throat points more to allergies. The mucus membranes in your nose tend to get pale and pretty boggy with allergies, but that's something you'd have to have your doctor look at for you with a scope.
Can be hard. A cold is a self limiting infection that will resolve in a week or two typically associated with a fever and generally not feeling well. Allergy on the other hand does not cause fever, usually lasts for weeks ( spring or fall for example) and does not cause other symptoms like achiness. There is a lot of overlap and in the fall and winter time you may experience both. See your doc for for hel.