Old events deleted from Calendar

I wanted to check when I had my annual physical last year so I could know when to schedule the one for this year. All events from about last April back were gone! I didn't realize that when I got my new iPhone, iCloud sync was automatically turned on, but when I went to my iCloud account, it was even worse. All events from last month on were gone! I need a permanent record of many of my appointments, so deleting old ones automatically does NOT work for me. How do I preserve ALL events on my calendar app, no matter how old they are?