Poor you. I have started suffering from insominia last June and for no apparant reason. Like u I wasn't stressed/depressed/worried about anything. It just happened one night and then I think the fear of it happening again was what did it. I ended up on sleeping pills but came off them 4 wks later as docs don't give you any longer than that.
Me and DP ended up sleeping seperately and still are!!
I tried warm baths/no caffeine/reading etc.
Nothing works because I worried about it all the time. I would panic thinking how tired I was going to be for work and that makes it worse. I am 29 wks pregnant now too. Since sleeping on my own I managed to stop the fear of not getting to sleep and have been much better for about 4 months now but I tried sleeping with DP again and couldn't do it cos all I do is listen to him breathing and I can't fall asleep. We are hoping that when baby comes we will just be too tired and will fall back into the routine of sleeping together.
Things I was told to try that do help:
If you sre still awake 20 mins after you get into bed, get up and do something mundane. Don't do anything that will get anything done like cleaning/ironing etc. Read the backs of shampoo bottles or tinned food in cupboards.
Don't nap after 3 pm
Don't read to get yourself to sleep/watch tv as this actually stimulates you.
No caffeine/food later in evening
Create a positive bedtime routine to wind yourself down and get used to going to bed to fall asleep, not to read/watch TV etc.
Try and imagine every bit of your body falling asleep from your toes upwards.
Some of these things help.
I should add just being pregnant though, it can be that your baby is awake and therefore your metabolism is on the go when you want to be asleep so pregnancy related insomnia just can't be helped.
All in all try not to stress about not sleeping as it will only make you worse, I used to cry my eyes out in frustration but after a while I just used to accept that I wasn't going to get much sleep and that it's not the end of the world and ususally I would fall asleep more quickley.
My doctor said most people suffer from insomnia for a short time and it ususally goes again. It's very rare for it to last long.
Hope you get some rest, I really do sympathise.