c# Httpwebrequest 获取网页过快 第二次得到的内容和第一次的重复

Question

Httpwebrequest 获取网页过快 第二次得到的内容和第一次的重复
每一次提交的post都不同，请大侠们给点主意，谢谢
public static string GetHtml(string method = "POST")
        {
            cookieContainer = cookieContainer ?? new CookieContainer();            HttpWebRequest httpWebRequest = null;
            HttpWebResponse httpWebResponse = null;            try
            {
                httpWebRequest = (HttpWebRequest)HttpWebRequest.Create(url2);
                httpWebRequest.CookieContainer = cookieContainer;
                httpWebRequest.ContentType = contentType;
                httpWebRequest.Referer = referer;
                httpWebRequest.Accept = accept;
                httpWebRequest.UserAgent = userAgent;
                httpWebRequest.Method = method;
                httpWebRequest.Headers.Set("Pragma", "no-cache");
               // httpWebRequest.Headers.Set("Accept-Encoding", "gzip, deflate");
                httpWebRequest.ServicePoint.ConnectionLimit = int.MaxValue;
                httpWebRequest.AllowAutoRedirect = false;
               
                if (method.ToUpper() == "POST")
                {
                    byte[] byteRequest = Encoding.UTF8.GetBytes(postData);
                    Stream stream = httpWebRequest.GetRequestStream();
                    stream.Write(byteRequest, 0, byteRequest.Length);
                    stream.Close();
                }
                
                httpWebResponse = (HttpWebResponse)httpWebRequest.GetResponse();
                Stream responseStream = httpWebResponse.GetResponseStream();
                StreamReader streamReader = new StreamReader(responseStream, Encoding.UTF8);
                string html = streamReader.ReadToEnd();                streamReader.Close();
               // 
                responseStream.Close();
                responseStream.Dispose();
                httpWebRequest.Abort();
                httpWebResponse.Close();
               
                return html;
            }
            catch (Exception)
            {
                return string.Empty;
            }
        }
C#HttpWebRequestHTML