Will loosing weight cause hair fall?

Sometimes. Usually this is an athletic, anorexic woman who stops having menstrual periods.
Alopecia. Studies show alopecia areata can be caused by stress and several other conditions such as atopic dermatitis, thyroid disease, collagen vascular diseases,vitiligo and STDs including syphilis. If you are sexually active go to MD for pregnancy test and full history and physical exam. .