It's normal to lose something like 1000 hairs per day. Try some strengthening shampoo and vitamin E, but otherwise I don't think there is much you can do. If more is falling out than that you can check with your doctor, they might be able to prescribe something.
That is normal hair loss and breakage. When you start to notice it on your pillow, that's when you need to consider seeing a doctor. Hair goes through cycles of growing, and one of the cycles includes it falling out. If you're not being overly rough with your brush, then you should be okay. But always use a wide-tooth comb when it's wet so it doesn't break.