I have just read your other thread about your mum. Hmm - parents are interesting, aren't they? DD and I have just come back from 5 days with my parents (half term). Neither of my parents mentioned my miscarriage (less than 4 weeks ago). Also got a little heated re. disciplining DD. They have always hated me getting cross with her but now they have spent the last five days with her, they realise that she needs telling off sometimes and told me to do it more!!
Sorry - personal rant! My point IS that mums don't see things as we see them, even if they are our mums. If you really really want a second child, that is very very valid - it's not really anything to do with her.
You say you struggle with diabetes, job, DS etc - I think the majority of people on MN would say they struggle with all that life throws at them. I don't know whether I am coming or going half the time and I only have one DC to look after. But people DO cope, and if your husband really loves you (and you sound as though your love for each other is strong) then that sounds positive too.
I agree with DDF - why not try really hard to show DH that you can cope for the next few months - and be open with him about what you are doing.
At the end of the day, I think it is your relationship with your DH that matters a lot more than your mum.
Well - that's my thoughts! Keep strong!