how to measure the distance between the peaks in a series of peaks

I am trying to detect the distance between the defined peaks of a PCG signal. and compare the measured peak distance and lable the each peak.

Also i want to define the each peaks 1 and 2, for example if the first peak is 1 then the second peak is 2 and again third peak is 1 and forth peak is 2.

Can you please help me to solve this two issues.