For months now my fingertips have been creased/wrinkled even when they're not in water (looks like they have been). what might cause this?

Various factors: Make sure you are eating a healthy diet. Plenty of fresh vegetables and fruits, moderate amounts of lean meats, and plenty of water....8-10 glasses a day. Also, watch your exposure to the sun.... Use plenty of sunscreen when you are outside. Lastly, find a good moisturizing cream and use it daily. All of this should help, but it will take some time. If you need more help, seek out a dermatologist.