what phase are you in? I assume induction?
in that case, no to rhubarb, yoghurt and as long at the fizzy water is sugar free i think it should be fine.
I know,i'm very random. I've always hated it. But back when i first started this i was seriously looking for a 'sugar' fix one day and someone, can't remember who, were making rhubarb tarts and just got the idea to microwave some with water and splenda. Cured the craving anyway.