I have symptoms of celiacs disease but don't have it due to just having a negative blood test, what could it be ?

Depends: It depends on your symptoms. Also, blood tests can be negative at some times and later can be positive. Depending on how severe your symptoms are, you can always see a gastroenterologist so they can get a full history, review your lab tests and see if they can help you with a diagnosis of celiac disease or something else that explains your symptoms.

Trial of treatment: Nobody knows for sure how reliable the labs are; they may have been done incorrectly or you may just not have a form of the antibody that they can pick up. Small-bowel biopsy's an idea, but nothing's stopping you from making a trial of a gluten-free diet for a month or so; that's really the burning question, and it's been recommended when the diagnosis is in doubt.

Symptom overlap: Loose stools & bloating are a common feature to many with gluten intolerance/CD. It is a symptom common to many other conditions also. Lactose intolerance, sensitivity to food additives (#40 red food dye),various other conditions can share this symptom. Not all blood tests are equally reliable & you didn't specify yours. I would be cautious and learn as you need about all the possibilities.