Hi and welcome to our community!
I'm sorry that you've been dealing with discomfort for so long. Symptoms are different for everyone, but I personally find that stress and anxiety can cause my IBS to act up until I'm able to calm down, and then they can still take a couple of weeks to go away. Stress can be such a powerful trigger for many people. A friend of mine once developed IBS symptoms that lasted for months, did all the tests, etc., and once the stressful period was over she was back to normal. The same thing happened to my sister-in-law, and both were diagnosed with IBS in the meantime.
Do you have any ways to manage the stress right now?
It could also be due to a trigger food that you still haven't identified. Have you tried keeping a food diary yet? (More info about that here: https://irritablebowelsyndrome.net/living/the-food-diary) Since we all have different trigger foods, keeping a food diary can be beneficial even if you're already following the Low FODMAP diet.
I hope this helps. If you like, please keep us updated on your test results and how you're feeling. Sending hugs, Karina (team member)