Cold sore help? what causes it? what helps?

I always get a cold sore or two at the beginning of summer and the beginning of winter normally on my bottom lip. I've heard this is from weather changes. Is this true? Someone else said that sun exposure can cause breakouts and I definitely go out a lot in the summer. So that could explain summer . Next how can I speed up the healing time of a cold sore. Like I said I don't get them a lot but they're bad when I get them. My lip swells up a lot and its extremely sensitive. One person suggested that once it breaks open to out raw table salt on it and it will clear it out. Is this true? And does it significantly speed up the healing? Basically is the pain from the salt on the sore going to be worth the results?? Thanks in advance!