Wow, good luck for your big day! I'm not surprised you can't sleep with all the excitement.
I often suffer from insomnia, and it's not a fun thing. I had months at a time with only sleeping half an hour to an hour a night, which led to hallucinations and all sorts. Not pleasant, I can tell you! Anyhow, it means I have had some experience with this. I tried all sorts of medication from the doctor, herbal remedies and relaxation techniques but very little helped. I have two bits of advice, though.
1. Try Night Nurse. Take a capsule at 8pm. I found that, if I did manage to get to sleep, this helped me get a good few hours of really restful sleep. Compared to other remedies which make you wake up feeling groggy, this was the best by far. Obviously, this is NOT a long-term solution!!
2. If you wake up and feel you can't get back to sleep again, don't just lie there. Get up, go to the loo, read a book, watch a bit of TV, have a cup of tea, clean the kitchen. Basically, anything that takes your mind off sleep. You might find that just going for a quick wee breaks the hold and you drop off as soon as you go back to bed, but if not, just do something relaxing for a while. I sometimes have a hot shower, which can help, too. Snuggle up under a blanket on the sofa and put something crap on TV and you might just drift off there.
I hope this helps. I can't imagine what I'll be like the days before the wedding!