Anytime a dog changes his behavior, first of all get him vet-checked as he could have some occult medical condition causing him problems and he has no way to tell you except by altering his behavior.
Once you have a clean bill of health, you can begin to work with him enriching his life with more exercise, puzzles to figure out, feeding him his dinner in a series of kong toys so that he has to work for his meal(dogs love these challenges), obedience training, more games and actual sessions geared toward training him to build up his self-confidence and decrease his anxiety/neediness. But first, be sure his health is okay. Once that is settled, you can help him.
__________________  Jeanie and Tibbe One must do the best one can. You may get some marks for a very imperfect answer: you will certainly get none for leaving the question alone. C. S. Lewis |