Is it an obligation to fast and make sacrifices for God? Or is it just a holy week thing? If it is an obligation, how often are we supposed to do it?
For fasting, see: Should Christians fast?
The only sacrifice in the New Testament is the dedication of one's life to God. "I beseech you therefore, brethren, by the mercies of God, that you present your bodies a living sacrifice, holy, acceptable to God, which is your reasonable service. And do not be conformed to this world, but be transformed by the renewing of your mind, that you may prove what is that good and acceptable and perfect will of God" (Romans 12:1-2). The idea of giving up something, such as not eating chocolate for a month, is not what was considered a sacrifice in either the Old or New Testament. Nor is the denial of things like this required by God. "Therefore, if you died with Christ from the basic principles of the world, why, as though living in the world, do you subject yourselves to regulations-- "Do not touch, do not taste, do not handle," which all concern things which perish with the using--according to the commandments and doctrines of men? These things indeed have an appearance of wisdom in self-imposed religion, false humility, and neglect of the body, but are of no value against the indulgence of the flesh" (Colossians 2:20-23).