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 your doctor.
Without the ability to examine you and obtain a history, I can not tell you what the exact cause of your symptoms is. However I will try to provide you with some useful information.
There are several causes of headaches. Headaches can be divided into primary and secondary. Primary headache disorders are headaches without a direct cause. 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, bleeds in the brain or clots in the veins of the brain, and others. A good physical examination and a CT scan or even better an MRI of the brain is needed to exclude secondary causes, particularly in someone who has new types of headaches or worsening headaches.
Primary headache disorders are much more common than secondary ones. Migraines are the most common. These are located on one side of the head and are often throbbing and associated with light-sensitivty and sometimes nausea. There are several other primary one-sided headaches. In a young otherwise healthy person, the headache is more often than not going to be primary, such as a migraine, and usually easily treatable, but again, secondary causes need to be excluded. Evaluation by a general physician/internist is recommended, with some sort of brain imaging indicated (CT brain or MRI brain) to excluded secondary causes. This is important in order to better understand the cause of your symptoms and what treatment would be effective. Depending on the nature of your headache, referral to a neurologist may be warrnated.
Thank you for this opportunity to answer your questions, I hope you find the information I have provided useful, good luck.