Just make sure you aren't pulling your bangs or hair tight when you're pinning and pulling it up. Tight pulls give headaches, sore scalp, and can make more hair fall out from being stressed. Also make sure you aren't using hair bands with metal crimps, use the all elastic kinds (if you're not already).
I know for myself, if I wear my hair up too much in a row I lose more hair, usually when I wash it in the shower or brush it. But it is because I don't brush it much/at all during days/nights I wear it up, and those are just the hairs that would normally be in my hair brush if I hadn't pulled it up.
People on average lose up to 100 hairs a day (so I've read and been told many times). How much are you noticing on average? If it is just a few here and there, I wouldn't worry so much.
Hair also falls out over time for new ones to grow back, in a cycle. Sometimes we just notice hair falling out more because those hairs tend to be on the same/close cycle, making it seem like we're losing a lot of hair.
There are a lot of medical conditions and medications that can cause hair loss as a symptom, but if you haven't changed anything recently and haven't noticed other medical symptoms of something new popping up, it probably isn't anything to worry about. It is better not to go into all the medical symptoms stuff unless you have real concern, because it tends to make people stress out more--which can cause hair loss, lol. Seems like you already do this, which is good.
I have super thin, baby fine hair myself, and am always worried about hair loss, but so far I'm not bald!
/emoticons/
[email protected] 2x" width="20" height="20" /> Make sure you are using a good shampoo/conditioner, maybe try some hair masks. I bleached/fried my hair a little shy of 6 months ago, and what honestly saved my hair and kept me from going bald... I bought the Matrix Biolage Keratin shampoo/conditioner, and also the treatment spray. It is meant for over processed and damaged hair. It is a lifesaver! I don't need it all the time anymore, just once a week or two. My hair has a lot more strength and I'm not having as much hair fall out. Before I fried my hair, I'd lose small handfuls in the shower each time, it was bad.