I don't know how to help you, just wanted to let you know that we are in the same boat with my 4 year old. I find that if he is worried about something, or ANYTHING at all has changed even the slightest bit, including it has been longer than normal since he has seen his Granny (his fav. grandma), that he wets the bed more. Normally, it's something bigger, like he was doing really good, stayed dry 2 weeks straight, and then he was soaking through pull-ups and the sheets and all just before he started preschool. He wet his bed every night for a month and half after that. He got better, then I got a new job, and the wetting the bed started over. His doctor said not to worry about it, some kids, potty train at night much later, up to the age of 8-10 years old!!! (UG if this goes on that long!) We too encourage min. amounts of fluid before bed, some is needed with taking his nightly meds and teeth brushing, and require him to pee before going to bed. Its the last thing on the list before he goes to sleep!
I would say to investitate to see if anything is bothering him, otherwise keep on encouraging and possibly go back to pull ups. Do you have a matress pad on the bed that doesn't leak water so you can at least save the matress???