Been waking up with a mild headache on my right side for 3 days, but goes away when i run or excercise.. scared of brain cancer, but my doc says no..

Sleep/breathing : Waking with headache is not normal and can be associated with a sleep disordered breathing problem. If you experience excessive daytime sleepiness you should get a sleep study to see if sleep is your cause.

No worries: You are unlikely to have a brain tumor. Try to improve your sleep habits, reduce caffeine intake and increase water intake. Usually, these simple steps will help.

Many symptoms: You describe many symptoms and studies that have been done (carotid ultrasound, echocardiogram) but no brain imaging studies. That is the definitive test to look for a brain cancer. That being said, brain cancer is highly unusual in a 20 year old, particularly in the absence of neurological symptoms (weakness, numbness, seizures, blurred vision etc.).