Could be many factors or being sick, but depending on which side of the hemisphere you're on, the seasons are changing and that can contribute to cold-like symptoms, but really, they are nothing more than allergies. You may have never gotten them before, but they can develop as you get older. I never had a single allergy to anything before I was 23 and now, I have to take an allergy pill every day, or I'm done for, especially when it's rainy and damp. For some reason, the rain kills me more than dry weather, wind, or pollen.
Could be heaters, turning heaters off, pollen, ragweed, rain, anything. You can try gargling warm water with some salt and vinegar. This will help coat your throat and guard against the bacteria/allergen that's making your throat bad. You can also try some water with lemon and honey to soothe it.