Thank you everyone, so much. Reassuring and has given me some perspective - and some good ideas too.
I think I am the sort of person who needs time alone, and I certainly don't get much at the moment. I am lucky that I do have a bit of time in the evenings although ironically I get lonely waiting for DH to come home and being unable to go out/exercise which is what I crave.
My worry re getting a job is that it will be me, not DH, who will have to do drop-off and pick-up, take days off for ill children, and continue to do ALL the housework. That sounds like too much! Because his career really does not allow him this flexibility and the hours are brutal. He appreciates me being a SAHM massively btw, it allows him to pursue his career and this will in the long-term have financial rewards for us all, hopefully.
I know that things will improve with time, I just need to hang in there. I think that their ages (2.5 and 4.5) are really challenging in different ways. By 7pm I'm a wreck (physically and emotionally) after a long day that feels like a series of conflicts to get anything done (meals prepared and eaten, nursery attended, playgroups, shopping, chores...) I try to pick my battles, I'm not inflexible although I do try to be consistent about what I expect of them.
I read Playful Parenting, I DO need to lighten up (I have a history of depression), but it just feels really hard to not get bogged down with the daily routine. Groundhog day, it feels like. I need to make it more fun, for all our sakes.
I suspect that it's worse because of the weather. I am looking forward to being able to send them out into the garden. They actually play together quite nicely most of the time, but they do seem to want me to play with them more than I'd like (I find a lot of the play boring). I think I also need to explore new activities that I might enjoy more, that would occupy them.
Lots of food for thought in this thread, I really appreciate you all responding.