I am not certain what you are doing, or what you want.
I usually create frequency vectors (the x-axis for a Fourier transform plot) this way:
Ts = mean(diff(t)); % Sampling Interval Fs = 1/Ts; % Sampling Frequency Fn = Fs/2; % Nyquist Frequency Fv = linspace(0, 1, fix(numel(t)/2)+1)*Fn; % Frequency Vector Iv = 1:numel(Fv); % Index Vector (For One-Sided FFT Plots)
The plots would then be:
plot(Fv,XX(Iv)) title('X-Axis')
or:
plot(Fv,abs(XX(Iv))*2) title('X-Axis')
depending on what you want, and similarly for the others.
See the documentation on fft (link) for details.