A cold often begins with a sore throat, followed by a runny nose and eventually a cough. If there is a fever, it won’t typically be very high. Mucus will begin thin and clear and can progress to thicker and darker. Colds tend to progress through phases and are gone within 7-10 days. When comparing to an allergy, cold symptoms are typically worse when you wake up and again in the evening when you are more sedentary.
The flu usually comes on more intensely than a cold. The symptoms can seem similar including the sore throat and cough. However, the flu usually produces worse body aches and a higher fever. It also usually starts to improve within a few days, even though you may feel run down for another week.
Allergy symptoms are more like a cold except that the runny nose is often accompanied by itchy feelings in the eyes and nose. The other main difference is that allergy symptoms are usually worse during the day and are better early in the morning and later in the evening.
Keep in mind that these are just guidelines, but hopefully they will help.