HopingCat - I don't think it is your subconsious telling you anything, it's just natural, especially as there has been a run on bad luck on this board. I too went to my scan a week or so ago and I was convincing myself that I couldn't be lucky third time round, but the scan showed that everything was absolutely fine, and I cried tears of relief. I'm sure you'll be ok.
Emma, what is it that you actually feel stressed about? Is it about something going wrong with the baby? (Sorry, I'm not very au fait with your history). I do understand, tho about feeling teary and being down, but remember, this is a really hard stage and it's difficult to feel happy about being pregnant if you are exhausted or sick. I'm still both, with two kids and work and I've been going crazy lately at my eldest as I just haven't had the patience to deal with her. I took myself off to my parents at the weekend and by today, I was feeling calmer and have hardly shouted at DD1! (She is a pain in the arse tho - and is pushing a lot of buttons at the moment).
In terms of stress affecting the baby, try not to dwell on it too much. Last year when I was pregnant with DD2 I had THE most HORRENDOUS time at work as I was chewed up and spat out by them and the stress was phenominal (sp?) and I was really worried how the stress was affecting the baby. I needn't have worried, she's a bouncing bubba now and no probs. Bear in mind too that the placenta will be kicking in at some point and your hormones will be fluctuating all over the place. Don't just think it's you. When it comes to depression, it's like a muscle that your brain flexes out of habit and it thinks, 'ah, I recognise this, I've been here before' and it does it out of habit. Just tell yourself that it is just your brain doing that and that you are fine and that your are not going to give into that way of thinking. This is really important. Keep your chin up - this stage will get better for all of us. Time doesn't stand still and things always change. You'll be alright love.