Posting the data will allow others to help but you can start by graphing the data in a histograms and looking at how it is distributed (does it look like a bell curve or does it have multiple peaks, outliers, etc) and/or by Q-Q plots. These might show why/how it is not normal, not just that it is not. Doing a run chart to show drift on the process will also be useful although youay already see it (or not) on your SPC