Nacho Grosso

I've got a problem with my shuttle, I can't understand why when I try to point it nose right to 45 degrees to set my desired apoapsis, it starts to wobble in its longitudinal axis and it turns completely uncontrollable. I tried to fix it adding more struts between the shuttle and the boosters as well as between the shuttle and the external tank, and adding more RCS thrusters and a SAS too, but it didn't work so much. Any ideas about how to fix it?