I Have Been Having A Lot Of Problems Falling Asleep

I have been having a lot of problems falling asleep at night. I work 8 hours a day, go home, change clothes and go for a walk for 30 minutes since it's getting cold outside. I try to stay as active as possible but the weather puts a damper on that sometimes. Are there any vitamins that I can take to help me sleep? Since July of this year sleeping has pretty much been slim to none with me. I don't fall asleep right away I toss and turn for a bit no matter how tired I am. I try to go to bed by 2100 but no matter what time I fall asleep I'm wide awake at 0100.