I was interested in computer science and my brother was working in this field. In addition I was sure about the future of this field. I was feeling I would be successful in this field, but unfortunately because of having two jobs I could not become successful through studying.
Your original was: was interested in computer science and my brother was working in this field and I was sure about the future of this field and I was feeling I would be successful in this field, but unfortunately because of having two jobs I could not become successful in studying.
Too many "ands". In english to use a word like and too often is not acceptable.