I promised the lord our God that I will fast for 7 days. What if I Broke that promise and ate?

This is my first time fasting. During the last passed 2 months I have been studying the Bible and working extremely hard to become righteous. Just this passed weekend I slipped into sin. Sex and drugs is what I gave in to. I believe the lord has condemned me because this passed Sunday after church I was highly irate for some reason. Everything and everyone seemed to irritate me. I threatened my twin brother with violence and I was terribly unloving to my 9 year old sister. Because of this I have decided to fast for the first time. Its only been one day and I'm feeling sick because I haven't eaten. I'm putting my trust in God to give me strength to endure this but I'm scared I'll give in to my desire for food. What is it that I should do?