Periodogram frequencies not matching with signals
The output you get from the periodogram are the power spectral density for the angular frequencies W in the range from 0 to pi. With the sampling rate Fs you can compute the frequencies f from W with: f = W * Fs / (2pi).

Be aware that you can only display frequencies from 0 to Fs/2 due to the Nyquist criterium which states that you need at least two points of a signal to be able to detect it.