Celery contains lots of fiber which is good for you but in excess the too much fiber from eating too much celery could lead to stomach pain, gas pain, gas, and even diarrhea.
You'd have to eat way too much celery for it to be a problem though and eating celery everyday should do you no harm.
I snack on celery everyday myself and have never had a problem and celery is good for you since it's rich in vitamins and other nutrients your body needs to stay healthy.