Foucault's+construction+of+a+discourse+for+the+discourse+of+sexuality

Ok, I am trying so hard to understand Foucault and write something but I can’t. First I want to admit that I didn’t see any point to what Foucault says about sexuality. But I am sure that I am wrong. So I will try harder. Specialists from the west started to research for the truth of sex. Sex is science and its experiment the confession. So they create sexuality’s discourse, a discourse inside the other discourses, pure human made. Inside this discourse there is everything connected to sex. And all these discourses are manipulated by the agency whose power is not hierarchical, flowing from the top down, but everywhere local. This is the system, everything with value exists in there and we create everything with value in it. Since people think, create and act inside the discourses there is nothing out of the discourses. Or is it? Ok and here are my questions: So there is the agency that knows more than anybody else, how they know more? Their knowledge must come from inside the discourses because nothing has any meaning outside them. So let’s assume that they construct everything and then they have the power to release it to the other people in any way they wish. I will assume that everything we know is inside the discourses, then how we can request the truth? What kind of truth we are talking about? I can’t understand how there is somewhere a truth that we have to find, since we are the ones who construct everything. So the truth is constructed as well, and we have the constructed truth. Or the agency has it. Of course we have it, how is possible to talk about sex and sexuality without knowing their truth? Is there a value to a concept that we don’t know what it means? And if we construct everything or let say the agency constructs everything how we know that the truth of all our constructions is the real truth? The pure truth? How do we know for sure that the pure truth isn’t outside the discourse? Finally, since we construct everything then Foucault is constructing a discourse for the discourse of sexuality.