Thanks for your question, and sorry to hear about your level of concern. First, if you are concerned about something, it's important to have people that you can turn to for help. Your parents are an obvious answer for many, but not all, people, and so please consider discussing this with them. Second, your doctor
is someone who is under an obligation and responsibility to help you, and it is therefore appropriate to discuss this question and any other questions with him or her as often as you need. Now, with regards to your question, there are many possible explanations, and most of them do not involve fatal diseases or cancers. Thin people, especially, will often have small lumps that are often lymph nodes that are readily palpable (able to be felt through the skin). These may change in size or character, but are usually just a part of you and are noticeable because you are thin. Next, there are many benign growths that can happen, with one of the more common being known as a lipoma, which is a fatty tumor that can easily be removed in most cases. There are other explanations too, so please speak with your doctor.