Why does sex isn't very interested to me?

Not interested in se. Do you mean why you have no interest in sex.We need more details if it has always been like this, if you are married and why sex is not interesting for you. I will suggest you start with your primary care physician and get complete exam to rule out any medical problem and also get gynecological exam.If no cause is found physically than you may need to see a therapist to help you.