A set of nonlinear differential equations describing the dynamics of an exciton-photon-carrier system driven by two external classical laser fields is established taking into account the interaction between the quasiparticles as well as the screening of the photon-exciton transition due to the presence of definite exciton and carrier densities. It is shown that both stationary and transient behaviours of the system are considerably influenced by the densities. While the exciton-assisted photon-exciton transition may lead to optical tristability, it, together with the exciton-carrier interaction, modifies the parameter domains in which the phase trajectories form a limiting cycle, a torus or a strange attractor. The system dynamics thus can simply be controlled by adjusting the exciton or/and the carrier densities which in turn depend on the level of the external optical pumpings. (author). 26 refs, 1 fig.