Awww sorry to hear that. Maybe a change of diet and keep a food diary to try and identify what foods might be triggering the diarrhea.
I've had tests like you but nothing wrong with bowel just stress!!!!
Tell your GP and try and get them to give you a referral to have it investigated. I have been suffering with bad diarrhoea the last few years and had to change my GP to get a referral to get it investigated. I have had blood tests, poo samples and a colonoscopy where they took a tissue sample from my bowel. I should be getting the results soon.