"But if I say I'll never mention the LORD or speak in his name, his word burns in my heart like a fire. It's like a fire in my bones! I am worn out trying to hold it in! I can't do it! "
I've always heard this verse preached like 'Your word is so wonderful that I can't hold it in, I have to say something'.
The Lord gave me a slightly different revelation on it, if you swallowed a glowing ember from a fire you would do anything to get it out of your body, it would be very painful. This is what Jeremiah meant, he could not hold the word of the Lord in OR it would burn him constanly, his only relief came through speaking it.