There are several medical conditions that cause night time sweats, so you really need to get checked out by your doctor. Some medications do as well. See your doctor regarding this and let's go from there. Below is a great website that has the causes of night sweats, read it and then see your doctor.
Hope this helps!
http://www.mayoclinic.com/health/night-sweats/MY00576/DSECTION=causes
May i ask, are you a male or female and how old are you? It doesnt say on your profile.
I ask as this was a troublesome symptom for a family member when she was starting the menopause. What you describe sounds identical to her.
Maybe you should go visit your GP and have a chat, see what they suggest. They may do a blood test to see if you are indeed starting your menopause, even if your fairly young it would be an idea to see the doctor for advice and maybe tests.