My 4 year old boy keeps wetting the bed?

My 4 year old son (just turned 4 in Jan) has been potty trained since he was 3. Recently he has been wetting the bed every night sometimes more then once. We wake him up 2-3 times a night to go potty and he pees and still he wakes up wet. I am pregnant and we are having a little girl due May 23rd. So i didn't know if maybe he is doing this out of anxiety, he used to have an occasional accident here and there but it has never been this bad. We have tried to cut back on his drinks, but he stays thirsty more so around bed time then any other time of the day. Has anyone else had this problem or have any advice, he has been checked by the doctors and they don't see anything wrong with him. He was diagnosed with ADHD a few months ago, by some quack of a doctor, got worse on the medication so I took him for a second opinion and the new dr undiagnosed him. Please help!