Sorry this is long. Please help me figure this out...
DD is nearly 7. She was a very confident baby and toddler - people used to remark on it at baby groups while she happily investigated without giving me a backward glance. I went back to work part time when she was 9 months old, she had no separation problems, was totally secure. We moved location, new nursery, absolutely fine. Started Reception, she was amazing; my complicated part-time teaching timetable meant that she went to 4 different settings on various days, but she knew her schedule and was fine. She used to get emotional sometimes on the afternoons I could pick her up, but that was it.
At the end of her Reception year I became a SAHM; I wanted to do the school run every day, and DS was about to start preschool. It has been brilliant for all of us, but since then DD is so different. Most mornings she's happy to go into school, and most of the time is happy. But sometimes in the mornings, or if I have to leave her for something I don't usually do, she gets extremely emotional, floods of tears, grabbing at me, running after me. She KNOWS I'm coming back. This happens quite a lot when I've been reading in her class. I do an hour a week, the same hour, I leave at the same time, and she very very often gets upset when I leave. DH and I used to go out occasionally and use babysitters (always people we know) - now she gets very upset if I even mention we might do that. She's only happy to be left with relatives, although she'll go to friends' houses OK. I'm about to start a part-time job (during school hours, no childcare required) and every time I mention it she looks at me like this 
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Today I took her to a sports workshop thing with loads of other kids, teachers and parents - a few of us went inside to get a hot drink as it was freezing. I should have told her where I was going, I realise, but she was doing an activity in a crowd and I didn't think she'd miss me. She was fine when I got back but didn't want to leave my side. Then I said I had to go back to the car to get something (car park visible from the pitch) and she had a meltdown . There were 70 children there and she was the only one who cried. She didn't stop crying even after I got back, it was like she'd worked herself into a state.
She's always been a fantastic sleeper (seriously, through the night from 11 weeks, never got up as a toddler, just fantastic) but now it takes a while to get her to bed, she says she's scared of the dark, she quite often comes down crying about little things and we have to get cross to get her to stay there (I've tried being nice and cuddly - I am nice! - it just makes her do it more - give her an inch sort of thing). I hate it. It makes me feel crap. She is a bit of a drama queen and at times I know she's trying it on, but while it's happening I think she genuinely is upset. If I ask her why she does it she doesn't know, she just keeps saying sorry.
Sorry this is long. She is a fantastic kid - if I read this OP I would wonder if something had happened, but I don't think there was any event that has precipitated this. It's so odd that it coincides with me giving up work, when it should have had the opposite effect! I just feel like I can't make her happy. I'm worried she'll get a reputation at school as 'the one who cries'. How can I help her feel secure again? What on earth have I done to cause this? Where has my confident little girl gone?
Any thoughts gratefully appreciated.