Craving onions could mean that you just love to eat onions because they are delicious to you.
But then again some health conditions can cause a person to crave onions as well.
Some health conditions that can cause a person to crave onions are things such as you're fighting an infection, or you have high levels of LDL "bad" cholesterol, or are running low on trace minerals.
Liver damage and other liver issues can also cause a person to crave onions.
So if you're constantly craving onions it would be best to go to the doctor and get tested for any possible health conditions.
Let the doctor know that you're suddenly craving onions so they can perform some tests because sometimes the issue can be health problems.