my breaks are lossing presure on first pump on 1999 Buick Century

my front break pads were replaced last fall and in the last month when i would prss the breake the break pedal would go almost to the floor but if i let my foot off the break and pump it agin the would stiffin up and work great

Asked by for the 1999 Buick Century
could be air in the system.
could be a wheel bearing failure in the front wheel as well.
could be a master cylinder seal failure.
at any rate, get it to a shop to have it pin pointed and a bid.