"Exhausted" means "very tired".

When you want to emphasize the word "exhausted", you can use adverbs like these:

I'm so exhausted.

or

I'm completely exhausted.

However, it doesn't sound right to say "I'm very exhausted". That's because "very" is already included in the meaning of the word: "exhausted" means "very tired". Adjectives like this are sometimes called "ungradable" or "extreme" adjectives. Here are some more examples:

• horrible
• enormous
• terrible
• amazing
• delicious
• excruciating