struggling to pump!!

Lola

lately when I pump, it seems like it's not working. like the shield will fill will milk and my breast will be too slippery to actually pump milk into the bottle. so I wipe it dry and it'll pump for a short time and get slippery again. this never used to happen. I cant get anything in the bottle. I've even tried different shield sizes. does anyone have any tips! my breast are so full but cant be pumped! I'm so frustrated.