Hair falls out more in spring and during fall.
Hair can also fall out a lot if you're stressed out, have had major illness, have had surgery, are pregnant or have had a baby, have anemia, take certain medications, have allergies, have yeast issues, sebbhorreic dermatitis or psoriasis on the scalp, or are manually aggressive to your hair or use really strong products: too high heat on blow dryer, yanking, scrubbing hard with a towel on wet hair, using silicone products, not conditioning enough, using too many products in hair, over processing with color and chemicals, having dry hair, etc.
Taking B-complex and multivitamins help, as well as iron. Most women are slightly anemic and don't even realize it, so they lose hair a lot - an iron supplement (and wash it down with something with high amounts of vitamin C, since vitamin C helps absorb iron your body). Drink your OJ and have plenty of calcium too (but the calcium shouldn't be taken the same time as the iron - calcium interferes with adsorption)!