caulking what am i doing wrong?

3 times in 6 months ive had to re do my caulking in shower/tub combo! i donrt understand whats going on any help? ideas? ty

Things need to be dry before you caulk...depending on the conditions, that may take several days. A fan in there can help.

Some caulks need to cure for several days before you can let them get wet, as well.

You didn't indicate what caused you to replace the caulk. What symptoms are you seeing that indicated you needed to replace it?

If the depth of the caulk is large, you should consider filling some of that space with foam backer rods.

Alcohol can be used to help clean up the surfaces prior to caulking.

Tile and grout is NOT waterproof, so hopefully, the surface (assuming there IS tile in this equation) below the tile was prepared properly with a moisture barrier.

If the caulk is turning black from mildew, they make mildew-resistant caulks.

Also, make sure you're using acrylic latex caulk for shower and bath.

You can always go to a pure silicone caulk, but it's more difficult to work with and clean up from. Silicone should last 10 years or more.