If the problem has appeared suddenly then something about the instrument has changed. The obvious first choice is a leak, and the second choice is that something in the keywork has gone out of adjustment. Re-examine your pads using a torch to illuminate the hard-to-see areas. Check the actual condition of the pads, one could be torn, damaged or loose. If this doesn't yeild the culprit then the problem could be one of adjustment. Adjustments don't normally change spontaneously without cause, so look for bent keywork or missing pieces of cork.
There are four most obvious places to check. These are at the top of the instrument, where the relationship of the G# key and the A key is important. The G# key should be lifted by the A key just after the A key starts to move. This is regulated by the adjustment screw on the G# key. Also at he top of the instrument check that the register vent is not blocked or loose. This can be done with a pipe cleaner.
At the centre of the instrument the relationship of the linkage between the upper and lower joints is critical and at the bottom of the instrument the adjustments around the crows foot under the right hand pinkie keys is vitally important. If you don't know your way around the keywork and are not confident that you can do this then you need to take the instrument to a tech or have it checked by another player who knows their way around the mechanism.
As I don't know anything about your skill level or knowledge of your instrument it may be that this advice is superfluous, but take it for what it's worth.