I'm sorry, "it´s been one year and 5 months since i dont know anything from you" doesn't make sense to me. I can't even rewrite it because I don't know what it means. Here are some sentences that do make sense and illustrate good usages of "since." "I don't know whether to offer you coffee or tea, since I don't know anything about you." "It's been one year and five months since I last heard from you."