What do I do when the conversion totally eliminated a couple thousand photos???? They are GONE.

ON my MacBook - this update LOST about 2,000 photos. Also, it totally jumbled the ones that DID import and assigned them incorrect dates. I am a photographer. Thanks Apple, for totally SCREWING UP IPHOTO. I am a got organizer, and all I get for "help" is - you should be using Photoshop, not iPhoto. iPhoto was GREAT for me. This version, however, has not alone caused me angst and anger, but list some clients' pictures.