My load balancer don't balance...!

You are seeing expected behavior. With your configuration BIG-IP is making one load balancing decision for the TCP connection not for every HTTP request. If you wish to load balance each http request to different pool members you must implement a OneConnect profile as explained here:

When a OneConnect profile is enabled for an HTTP virtual server, and an HTTP client sends multiple requests within a single connection, the BIG-IP system is able to process each HTTP request individually. The BIG-IP system sends the HTTP requests to different destination servers as determined by the load balancing method. Without a OneConnect profile enabled for the virtual server, the BIG-IP system performs load-balancing only once for each TCP connection.