Excessive amounts of caffeine or chocolate can also cause outbreaks, anyone who suffers with recurring coldsores should avoid both.
The first one could have been caused by any of the reasons mentioned before. The 2 after that may well have been caused by reinfection. You must be extremely cautious about anything that has come into contact with a coldsore. Throw away your toothbrush and toothpaste, same goes for lipstick or lipsalve that came into contact with any sore. Wash towels and flannels on a high heat, and make sure you soak all mugs, cups, cutlery etc in very hot water too. That way you'll cut down your risk of recontamination, and also the chance of spreading it to other people in your household.
One of the best things for helping with this is those Compeed plaster things that came out recently, not only do they really help with the healing time, they also provide a good barrier and stop you from messing with/touching your coldsore.
I hope you get shut of them soon, they really bring you down don't they!