It sounds like you are not initializing your other plugins inside the afterRender
callback as detailed in fullpage.js documentation:
afterRender()
This callback is fired just after the structure of the page is generated. This is the callback you want to use to initialize other plugins or fire any code which requires the document to be ready (as this plugin modifies the DOM to create the resulting structure).
$.fn.fullpage({
afterRender: function(){
//your plugins initialization here
alert("The resulting DOM stucture is ready");
}
});