Cold sores are caused by the Herpes virus and there's no cure for it, but there are things you can do to help it heal faster. There are several cheap home remedies that people swear by including using toothpaste like you mentioned, but it really depends on the individual and what works for you. For me, putting ice on it when I first feel it coming on helps a lot. Ice not only brings down the inflammation, but also prohibits the virus from multiplying in that area, keeping the actual sore from being too big. Once the sore does breakout, then I use a lysine ointment on it and take extra lysine supplements until it heals. It usually goes away after a few days. There was a clinical study at USC that shows lysine ointments help cold sores heal 50% faster and is better than most other types of ointments on the market. I don't know if it would work for you, but it definitely seems to work for me. Good luck!