Bismillahir Rahmaanir Raheem
Al Jawaab Billahit-Tawfeeq
The name "Sarah" pronounced "Saarah" in Arabic is a perfectly good name. It was the name of the wife of prophet Ibrahim (AS). Not only is changing this name not required but it would also be disrespectful believing that this is the cause of difficult times.
While names can have an affect on a person, this name "Sarah" is virtuous. If you are called "Ser-rah" with the English pronunciation then it is recommended you correct as much as possible but this is not an important factor in this case.
Fortune-telling is forbidden in Islam and holds no value in its results. It is neither heavenly, spiritual nor scientific. It is merely a farce where the weak are exploited. There are clear warnings in Ahadeeth about those who seek it, give it, listen to it or participate in such things where their Salaah will not be valid for forty days and in another narration where the guilty have disbelieved in what was revealed to the messenger of Allah. Please see http://www.muftisays.com/qa/question/2221/those-who-tell-us-our-presentfuture.html
Please see similar answers on names such as http://www.muftisays.com/qa/question/35/answered-keeping-any-name.html
A good practise would be to perform Salat Al-Hajah - the prayer of needshttp://www.muftisays.com/qa/question/2079/salaatul-haajat-.html
And Allah knows best