I had the same thing! If 20 or 30 minutes passed and I still was awake, I would just get up and do something that wasn't terribly stimulating, such as flip through a magazine or re-read a chapter of a book I had already read...
Do you have an urn? I would turn the urn on before bed, so that the water is already boiled, and keep some crackers on the table... it will then be no big deal to make some tea in the middle of the night (I found chamomile with a little bit of honey to be quite soothing) and grab a snack. That's what I would do...I'd give myself up to 30 minutes...then go downstairs and have tea and crackers, then go back to bed...sometimes I'd repeat that scenario two or three times but eventually I'd fall back asleep (sometimes 3 or 4 hours would pass!). I started to sleep better in the middle of my 2nd trimester.
Hang in there...it will pass.