Hey Joanna.
First if all, a dozen means 12 so you you would say " two dozen eggs" because the word "dozen" works just like "hundred".
When talking about specific numbers, we say "a hundred", "two hundred", "three hundred", etc. In the same way, we say "a dozen", "two dozen", "three dozen", etc.
If we are talking about some unspecific large number, we can say "dozens of" or "hundreds of".
For example:
-Hundreds of children missed the first day of school because of the newspaper error.
-The storm caused dozens of empty bottles to wash up on the beach.