My Dog doesn't stop whining, HELP!!?

I have a cross Boarder Collie with Poodle and he is almost 18 months old. To be honest I am at my wits end with the dog, he whines constantly for no reason. He has had a full check up with the vet and there is no medical problems with him at all. Not only does he whine ALL the time but he also follows me everywhere I can't even go to the toilet without him following me at it driving me MAD!! He goes out 3 times a day so he is getting enough exercise and I have 3 young children that play with him a lot and he adores them, this is my problem I do love him as much as he annoys me and I know that I couldn't ask for a better family dog it's just the whining that is driving me CRAZY!!!

Please help and advice would be great.

Thanks :-)