it gets better, I promise!
It's important that both you and he realise it's all due to hormone surges and you aren't actually going mad.
On the practical side, take your fiance to the 12wk scan - it'll help it feel more 'real' to him and hopefully make him more tolerant.
Has he got a decent book he can refer to so he feels involved and informed? The free NHS pregnancy one is pretty good - no-nonsense, easy to understand but not patronising.
Also I guess that you'll formally announce the pregnancy after ther 12wk scan, so colleagues etc will start cutting you a bit of slack, which always helps.
It's a shame your mother can't make it but if there's nothing that can change it there's not much point getting het up or blaming her - you and your chap will manage fine .