Mine's the same Moomin, not hard and just looks like I'm a bit podgy unless I whip my top up to have (yet another) look! I have put weight on elsewhere though unfortch.
Nights were OK thanks, they;re finished now. Last night was rather eventful, I got punched by one man, called fat by another and then a lady poo-ed on a table. But on the other hand a patient gave me a christmas card with such a lovely message inside that I cried in front of her and she rubbed my back!! 
TTL, I'm a student nurse not a real one just yet! :) But I guess it's perfectly possible that you might have one ovary. I'm not sure if this would necessarily mean you'd skip every other period, it would appear to make sense though I was under the impression that ova were released randomly from ovaries not necessarily left, right, left, right. But you might be unusually symetrical. So basically, I don't know for sure and no-one would unless they did exploratory tests. But if you're worried speak to your midwife/GP. I'm sure it's nothing to worry about, as obviously, you have concieved! And we develop thousands more ova than we could ever use in a lifetime so it's not like you'd run out.
On the other hand the sonographer may not have been able to get a look at your other ovary so may have been wrong anyway. Ask at your next scan perhaps. Are you worried about it? Sorry I couldn't be more helpful :)