I just had my ring resized and it fit yesterday. Woke up this morning it was way too small. Possible causes of swelling?

Water retention. I get this sometimes as well. It happens when i eat a particularly salty food. This causes your body to retain water. Also, you will probably find that on cold days your rings are looser than on hot days. Don't exceed the recommended amount of salt per day and drink plenty of water so your body can eliminate the excess sodium. Msg in asian food will also cause this.