Sink is leaking. I already replaced o-ring so what to do?

So my bathroom sink had been leaking a few months ago, and I found out that it was because the o-ring was corroded. I replaced it, and the problem stopped for a few months. But recently, i noticed the faucet was leaking again. I checked the o-rings and they were fine. BUT, WATER WAS STILL LEAKING! This time, from under the sink. I don't know anything about sink components, but under the sink there are the two tubes, one that connects to the hot water valve, and the other for the cold. The water is leaking between them. What to do?