Words are like songs. They can get stuck in our heads so firmly that it's hard to think of an alternative. That's why we often find that all our characters are repeatedly sighing or scratching their heads thoughtfully or feeling shivers run down their spines. This happens to every writer from time to time, and I am no exception.
Don't worry too much about this type of repetition while you're writing your first draft. It's more important to get the story down than to make sure every word is perfect. But, as you read through that first draft, make a note of any words you think you are seeing too often.
This is when the FIND facility in your word processing software becomes invaluable. Use it to find every instance of the word or phrase you're worried about. Then look at each one and see if it's possible to say something else instead. A thesaurus can be useful for inspiration - the one built into Word does the job well. . It also helps to think of alternative body language to show a character's emotions. For example, people don't always scratch their heads while they are thinking. They may rub their chin, bite their bottom lip, chew the side of their thumbnail, stick out their tongue or gaze into the distance.
But you don't have to remove all repetitions. It's perfectly all right to use a word or phrase more than once, especially if the instances are well apart or you are using a particular mannerism to build character. Also repeating a word several times close together can sometimes add emphasis or improve the rhythm of the sentence. For example, "He walked and walked and wallked" is a valid alternative to "he walked for a long time" and would definitely be my first choice for a story designed to be read aloud.
Repetition is a valid tool in the writer's tool kit Just make sure you're using it deliberately rather than accidentally.