Hi Milly
Your post absolutely chimed with my experience. Nice to find someone who will understand. My friends all seem to have high powered, high achieving jobs as does my DH.
I'm a SAHM with 2DCs and I haven't worked for 16 years
I was really bright at school but haven't done anything with my qualifications. I was ill with migraines when I got married, then wanted to start a family so never went back to work. I had PND after DC2 which was just awful, the worst time.
I went for a job interview last week for a job in a school. In theory I met the criteria but from the reactions of the interviewers I just don't say the right things having been out of work for so long. It feels like there's a secret language that I should be able to speak. Will run it all past a high powered friend when I've stopped cringing.
I really want to contribute to society but I feel I've just left it too late and no one will take me seriously now. I'm a bit in awe of you, you've got a job! Believe me, that is no small achievement!
I think I'm going to have to content myself with being the best mum I can be, (which I find hard going) and sorting out the mess which is our house. It all went to pot when I was depressed. Everything just stopped, the piles of stuff all date from then, so quite depressing going through it all. Life just stopped 
Anyway, getting off the subject. I didn't get the job, no surprise there. Maybe it was a blessing in disguise though. Don't know if I would cope with it all (and it was part time) and I need to be well for my family. I'm in a good patch at the moment but I don't know if that will continue.
I used to be so so sad about this great career I wasn't going to have. I could cry buckets thinking about it. I used to want to go into drug development. I could have done something so useful. But this is the hand life dealt me and the result of decisions taken along the way, which weren't the right ones really. But would I have met DH, had the friends I've got, maybe I would have moved away and not been with my family so much. Work isn't the only way we can contribute to the world, but it is the one that seems to be pushed and emphasized more than any other. But how much of that is just on economic grounds, everyone should be an economic unit.
I've had a lot of counselling and I don't feel quite so distraught about it, but there will always be a sadness there. So, I know how you feel. Have you had counselling or would you consider it? It helps just to blurt it all to someone, all the grief and frustration... Take care, my dear x