Is this cluster analysis / prediction?
I think your process is not really a cluster analysis problem, but instead a time series analysis problem. You have some process that is measuring a value ($Y$ variable) at different points in time ($X$ variable). I would suggest using a Shewhart Control Chart or something similar to understand the process that you have. You should also do analysis on the distribution to ensure it is normal, or use the CLT to enable the data to move towards normality.