Barca crashed to their third defeat in four games when they lost to bitter rivals Real Madrid on Saturday for the second time in four days.
Real also ended their Copa del Rey hopes in midweek, while they face a battle to stay in the UEFA Champions League after losing 2-0 to AC Milan in the first leg of their last-16 tie.
However, Alba insists they were unfortunate to lose to Madrid and that they still have the belief that they can overcome Milan in the Champions League.
"We leave without a point but we still have a good lead over Atletico and Real Madrid. It was a very even game and the fair result would have been a draw," he said.
"We have been able to have possession, but in long balls and set-pieces they have caused a lot of damage. We need to give everything and more to go through the tie against Milan but we still believe in ourselves."