The doorway-window representation of sequential pump-probe spectroscopy, derived by solving the nonlinear exciton equations, is used to study exciton dynamics in molecular aggregates. Exciton relaxation is incorporated through a multilevel Redfield relaxation superoperator calculated using the Brownian oscillator spectral density for the collective phonon coordinates. Optical pulses are included using a mixed time and frequency domain (Wigner spectrogram) representation. Numerical results are presented for a five-chromophore model aggregate.