'98 Nissan

I have a 1998 Nissan Sentra with 136,000 miles on it. It's been running great up until the last 6 months. My battery and break warning lights flashed for a while whenever I accelerated on the gas. Well I found out about 3 months ago this was my alternator going bad, which it did and I got it replaced with a brand new one. Well all's been great until 2 days ago I was on a trip driving about 60-70mpg for about 1 hour(the first long trip since my car's been fixed) and my break&battery light came on again and the airbag light was flashing. So I turned around, when back in the city, driving city speeds, slow, the warning lights went off. I knew I had to take it in, just needed the time, and it was driving fine. Well today, 2 days since the initial problem from the attempted road trip, the car just died. Had to get it towed to a garage.
My question, what can be the problem becides the alternator. I have a hard time beleiving that after a brand new alternator was put in the car, 3 months later the same exact events happened. And if it is the alternator, is their something happening that can destroy a new alternator?