I agree with having your doctor run a full blood panel on you. I can completely empathize; I've been experiencing this as well around my hairline. I start to get a widow's peak on both sides of my temple w/ the hair falling out, then it grows back. It's been doing this on and off for over two years now. Absolutely nothing came back out of the ordinary on my blood panels, so my doctor was at a complete loss, as well as my dermatologist.
What HAS helped me is taking a Biotin supplement. I take 1,000mg a day and that has definitely helped. I notice that if I slack off on the supplement, the hair falls out again.
If you google hair loss, there are literally hundreds of various ailments that can cause hair loss so it's not an easy thing to figure out if the blood panels come back fine. I guess I've attributed mine to hormones (I turn 43 this month) and the fact that baldness runs in my family. THANK GOD I was born with a TON of hair so I've been able to change my part around and hide the loss for the most part.
I wish you luck in figuring this out!!