"The thing on my shoulders..." I know you're trying to use strong language, but "it's a shit" just sounds funny. I suggest trying to rewrite the whole sentence and looking for other imagery. The second sentence is fine. "I've lost the last two years of my life." or "I've lost two years doing this." I'm not sure what you mean with the fourth sentence. Could you be a little more specific about what you want to happen in the future? "If I don't go crazy, I'll age prematurely." I think this is what you meant. You could also use "I'll either go crazy or age before my time."

The first example is a failed attempt at using a vulgar English slang phrase. These types of phrases are common in most languages but, as in your example, would sound ridiculous and comical if used incorrectly. Using street phrases, colloquialisms, and so forth require a degree mastery of the language; otherwise, they should be avoided until you know when, where and how to use them. Example two is fine. Three... I've lost the last two years of my life. (agreed) Four... I must prepare for the future. (not sure exactly what you mean) Five... If I don't go crazy first, I'll enjoy becoming older.