I second the Melatonin suggestion. We used it occasionally on our son, when he's so wound up we know he won't go to sleep. Our pediatrician recommended it, and from all the reading I've done about it, there are no worrisome side effects.
Regarding the "opening the door". My son used to always be able to go to sleep with his bedroom door closed. But just in the last year or so, he has wanted his bedroom door open when he goes to bed. So, we leave it open, and he was more willing to stay in his bed then. I think it was a nighttime fear, of some sort.
I hope it starts getting better for you!