I totally understand your frustration. I'd been back and forth to the GP for around a year. I was having really bad night sweats, felt really tired all the time. Bloods all came back ok. 
In July I attended A&E, I woke in the morning with really severe chest pain which travelled up my neck and to my left arm and Jaw. Had chest X-ray and nothing showed. Had some bloods and I had an elevated Troponin. They sent me home with naproxen and said I had pericarditis. The next day the pain was bad so I attended again. Had more bloods that showed I had an elevated D-dimer so I was admitted with a suspected Pulmonary embolism. Started blood thinners and was discharged with an outpatient CT scan. This is the point my tumour was found. 
I can only say persist. If things don't feel ok for you, press for answers. I felt like a massive hypochondriac- I was doubting myself that my symptoms were real. But here I am with a big tumour nobody expected to find! Now waiting for major surgery. 
I work in healthcare so I want to reassure you that the majority of the time these things are nothing to worry about, but if you are experiencing pain and other symptoms with no answer as to why, push push push! Wish I had done sooner x