Emma, if you're feeling nauseous after eating or worried about something else, you really need to talk to your doc. He can examine you and either give you guidance or put your mind at rest.
The word crepitus normally refers to a sound . So for example, it can be used to describe the creaking, grinding or popping sound sometimes heard when a knee joint moves backwards and forwards ( if it's without pain, normally no problem). It can also refer to the crackling sound in the chest of a person with pneumonia.