 [ Symptoms ] can anxiety cause schizophrenia [ Disease ] well the first thing i have to ask is is your daughter sexually active if so and she is missed a period then it might be wise for her to take a home pregnancy test at age 15 the menstrual cycle is not necessarily settled in yet irregular periods are not uncommon in that age group and the stomachaches and nausea could be due to stress or anxiety in other words i would not jump to any conclusions if your daughter is not pregnant and the other symptoms do not go away then it is worth a trip to see your primary health care provider he or she can investigate the cause of your daughter is symptoms and recommend treatment wishing you both all the best