You need to see a doctor and have some blood work done. In the mean time, I would suggest some multi vitamins and using a system called Nioxin. It is a shampoo (to cleanse the scalp) a conditioner (to condition and ready the scalp) and a Bio-nutrient Treament (to nourish the scalp). It is a system for balding men and simply helps to slow down your natural regeneration process. It will, quite frankly, keep more hairs in your head! It works very well, too.
I experienced Alopecia Areata during a stressful time in my life and I went to the dermatologist who simply said, "What you have is Alopecia Areata, it's when your hair starts to fall out. We don't know why it does but it does. Fill the script for some drops and if it doesn't help in 3 months, come back and see me. blah, blah, blah....)
Well, I thought, "Durh, I'm a hairstylist I know it's Alopecia Areata and quite frankly I could BE BALD IN THREE MONTHS!" So I threw the script in the trash, went and got on Nioxin and never looked back!!
But again, I would stil have the bloodwork done as losing hair from all over the head and not just in patches could be signs of something more serious than stress. So, do get that done and run out today and get the Nioxin System. Make sure you use all three, shampoo, conditioner and treatment!
Get everything in check and it will come back!
Good luck!