Abstract: Modern multi-dimensional spectroscopy offers a unique look "under the hood" allowing us to probe the dynamics of excitons in semiconducting systems. In this talk, I shall review our recent quantum stochastic model for spectroscopic lineshapes in a co-evolving and non-stationary background population of excitations. Starting from a field theory description for interacting bosonic excitons, we derive a reduced model whereby optical excitons are coupled to an incoherent background via scattering as mediated by their screened Coulomb coupling. Such processes include intra- and inter-valley excitons. The Heisenberg equations of motion for the optical excitons are then driven by an auxiliary stochastic population variable, which we take as the solution of an Ornstein–Uhlenbeck process. Here we discuss an overview of the theoretical techniques we have developed to predict coherent non-linear spectroscopic signals. We show how direct (Coulomb) and exchange coupling to the bath give rise to distinct spectral signatures such as phase-scrambling, excitation-induced dephasing, and excitation-induced shifts. We also discuss mathematical limits on inverting spectral signatures to extract the background density of states.