Thanks for using the forum. I am happy to address your questions, and my answer will be based on the information you provided here. Please make sure you recognize that this forum is for educational purposes only, and it does not substitute for a formal office visit with a doctor.
Without the ability to examine and obtain a history, I can not tell you what the exact cause of the symptoms is. However I will try to provide you with some useful information.
A normal, noncontrast CT does make it slightly less likely that a tumor is present, but a CT is only so good at detecting masses, which an MRI with contrast is much better. It is also important to realize that there are many reasons people have headaches. When headaches occur, it is important to determine the etiology of the headache. Headaches can be divided into primary and secondary. Primary headache disorders are headaches without a direct cause (such as migraines). These are diagnosed after secondary causes have been excluded. Secondary headache disorders are due to an underlying problem, there are many many causes but some include medication side effects, systemic illness, nervous system infection, tumors, sleep apnea, bleeds in the brain or clots in the veins of the brain, and others.
Primary headache disorders are much more common than secondary ones. There are several primary headache disorders, over 50 different types. One example is a migraine which is a pulsating throbbing one-sided pain with nausea and discomfort in bright lights that lasts several hours. This may be what you are experiencing.
I would suggest that you be evaluated by your primary care physician. You may need an evaluation by a neurologist who has an interest in headaches.
Thank you for this opportunity to answer your questions, I hope you find the information I have provided useful, good luck.
i forgot to mention that im a 22 yr old male and not over weight and in pretty good shape i do smoke but do not drink or do drugs.