There are several reasons you are receiving a large number of alerts, here are the top 3:
1) Be sure you are tracking only one Representative URL for each page template / page type. If you are tracking 100 pages that use the same template and there was a single change, you would receive 100 alerts.
2) If you have any dynamic content such as news feeds or advertisement code, turn off the page size monitoring.
3) Reduce the frequency of monitoring when configuring the Representative URL. You can reduce it from Hourly to Daily or even Weekly.