Well, if its that young and hasnt eaten "in so long" and you only feed them butter worms and a multivitamin once a week, there are a few strong possibilities here. For one, it probably has a series of very serious nutritional maladies. Frogs that age need to eat every day or two, and need a calcium supplement every other feeding to promote all that bone growth going on. A droopy jaw is a sign of metabolic bone disease.
You also may have injured its jaw trying to force feed it. how did you pry its mouth open? Ive had to force feed babies, and the response to me sticking the corner of a playing card between their lips was that they opened their mouths rather than having to pry anything. Also, a nutritional malady may have caused the jaw bones and muscles to be weakened, thus furthering the possibility of injury where a healthy frog would have been fine.
Having sticky food stuck in its mouth for two days probably didnt help the situation. But, a healthy frog should still have been able to swallow it as Ive fed sticky pacman food to my frogs several times.
Looking at the picture, the shape of the mouth appears injured...what did you pry its mouth open with?

You cant get nightcrawlers in Canada?

Pacman food has worked great for my frogs from the get go.