Oh popsycal. This is really starting to get you down now. You need to sit down with DH (when DS) is in bed) and talk this over with him.
As you know I teach part time (3 days a week) since having DD.
Financially - decide on number of days you want to do. I do 60% timetable but this works out at more than 60% normal salary, due to less NI and tax. And your threshold will still be on time too. You can choose whether or not to pay your pension still. I do for the security later on but my salary is still fine. I amm on top of normal scale now (no threshold) and have no responsibility points - I bring home just under £1000 a month.
You have to tell DH how you feel very very clearly. Teaching is not an easy option as you have so much work to do at home too. You need to make this very clear - can you try and write down how much you have to do compared to how much time you spend with DS (and DH for that matter). Maybe that will clarify things too. And be brutally honest with him about the way YOU feel about it.
It may also be worth looking on your union's webssite for more information too - I know the NASUWT site did have some good stuff on it when I wanted to look; or talk to your union person at work. I e-mailed the main guy in the area for info and they were really good as well.
Get as much information as possible so Dh knows that this is NOT a whim and you are really stressed as things stand.
Good luck and don't hesitate to ask for any more info, if I can help.
(Hulababy - formerly CnR)