my bf's cousin had a tumor caused by regular intake of artificial sweeteners. She was diagnosed with diabetes at 9, and by 19 was having severe headaches, which after MANY doctors ignoring the symptoms, led to an mri and diagnosis of tumor on the audio/visual nerve. She had a surgery with some complications, but has made an almost full recovery now, and now replaces sweeteners with limited amounts of sugar/honey and careful monitoring.
I have been worried as I have had the same symptoms as you have, and still cannot get a scan to rule anything serious out.
Went to a neurologist about the headaches and was advised to take magnesium and B vitamins. I also think dehydration could be partially responsible. Haven't started the vitamins yet but perhaps that will help.
also the thyroid could be causing a lot of your symptoms.