Since I only test Wink once a week, I'm using the larger 28 gauge lancets to poke with. These larger lancets are often labeled "For Alternate Site Testing" on the box.
I think it's much harder in colder weather to get the ear warm and a blood drop to form. At least it is for me.
Make sure your hands are warm enough before you touch your cats ear. My hands get really cold in the winter so I have to warm my hands first before I even start the testing process.
If your cat is dehydrated, that could make the blood flow slower and make it harder to get a drop to test.
Put a tiny dab of Vaseline on the ear before you poke, wiping off any excess. This can help the blood drop to form more easily. It kind of makes it bead up.
Try paw pad testing. Some people find this easier than ear testing to get blood. Depends on if your cat likes their paws touched.