Keep Session with fXML

Hello, I'm from Brazil, so apologize about the bad English.

I'm trying to use fXML to first authenticate then to retrieve information form a website.

The problem is that the session is not kept from a call to the other.

The code piece that matters is bellow.

$login  = new fXML('mywebsite?user='.$user.'&pass='.$pass, 5, TRUE);
		
		if($login->error_code == 0){
		
			$url = 'mywebsite?action=ChamadoCadastrar&estabelecimentoid='.$estabelecimentoid.
						'&motivoid='.$motivoid.
						'&tipon3='.$tipon3.
						'&solicitante='.urlencode($solicitante).
						'&descricao='.urlencode($descricao);
						
			$xml = new fXML($url, 5, TRUE);

When it calls "$xml = fXML($url, 5, TRUE);" the user is no longer logged in.

Can anyone help?

Thanks in advance;