I myself also a newbie too, but I will try to answer anyway
AFAIK without PDO enabled, Yii won’t work. I’ve tried it.
There is no difference in accessing, operating db with sqlite, mysql or other database. The only difference is the settings in configuration file.
If there is no way to activate the PDO I think it would be better to stick to CI currently. But I think you can still learn Yii. I always believe that learning new things will always bring benefit to ourselves.