I have had cold sores as long as I can remember. Picked them up somehow when I was very little. Probably from drinking after some other kid who had it.
I take Valtrex every day. It's the same stuff they prescribe for genital herpes. It's reduced my cold sores from 10 a year to 1 a year, and the rare one I get heals faster.
If you don't get them often enough to justify taking it every day, get a prescription to take as needed. Then as soon as you see the first signs of a cold sore, you take a dose. You only take it as long as you have the sore, then you stop again. It doesn't prevent them, but they heal much faster.
The everyday stuff I take is 500mg, but when I was doing the take-as-needed strategy, they were the 1000mg horsepills.
None of that over-the-counter stuff like Abreva works for me.