Calendar deletions

Hello, I have a 3GS, IOS 6.1.6, total phone storage 3.5 GB, 2.7 GB used, icloud storage 5.0 GB, 4.7 GB still available. The EVENTS on my calendar only go back 6 weeks or so. The rest have disappeared from calendar section. My last auto icloud update was this am. Any ideas on this...not enough storage? Every few days a few more days of events disappear.

I never have retrieved anything from icloud, how do I transfer past events back to phone calendar.

Thanks in advance for your help!