i've already used my credit card to buy stuff in the PS Network Store, but im trying again now and it says that the info of my card is incorrect. wtf?

check the expiration date on your card..this has happened to me before, I had a week left until my card expired and it gave me some invalid error when I tried to purchase something
also make sure you didn't delete or change your card info on your account

I remember a few months back a buddy had this problem. We triple checked all his info and it was years away from expiring. He tried again a few days later and it worked flawlessly. Maybe try again tomorrow?