Normally urine is contained within the bladder and prevented from leaking out by the urinary sphincter. Some dogs develop urinary incontinence which means a loss of urine through lack of urinary sphincter control. That is, urine will dribble out especially when lying down and sleeping.
We see this more commonly in older, overweight, larger dogs, and speyed bitches, although these factors on their own are not the cause.
Fortunately, after excluding other underlying problems your vet can prescribe safe and effective treatment.
There is no need to put up with damp bedding or urine scalding which is not pleasant for you or your pet.
Get this problem attended to right away by your veterinary surgeon.