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.
Trouble with memory in younger people such as yourself is uncommon, but there are causes. One that comes to mind is low thyroid function, what is called hypothyroidism. Low thyroid function causes fatigue, weight gain, cold intolerance, constipation, and memory/concentration problems in addition to several other symptoms. Another possibility is anemia, which can cause severe fatigue and thinking trouble. In addition, other causes include certain vitamin deficiencies. These can all be diagnosed with simple blood tests.
Another group of problems that can cause thinking problems and fatigue are psychiatric. This is not at all to say you are crazy or making anything up. Clinical (medical) depression and anxiety can sometimes be expressed not in sad or depressed feelings but rather in thinking troubles and fatigue. Treatment improves this.
Certain people live into adulthood with thinking troubles that are later diagnosed as learning disabilities or attention deficit disorder (ADD). Many people think of this as a childhood disorder but it can start in childhood and not be diagnosed into adulthood.
Finally, traumatic brain injury can lead to cognitive trouble depending on the location of lesions. Also, TBI is a risk factor in developing epilepsy.
Without further information about your headache, it is difficult to provide you with adequate information. However, it is important for you to understand that if you have not experienced headaches in the past and you are now having new head pains, seeing a neurologist is a good idea, just to make sure there is nothing serious causing this pain. Imaging of the brain and sometimes then neck may be indicated depending on your exact symptoms, your physical examination, and other factors.
I highly recommend that you follow up with a neurologist to discuss your symptoms in more detail. You may need an EEG to evaluate for seizure potential. Also, a repeat MRI may be useful if one has not been done recently.
Thank you for this opportunity to answer your questions, I hope you find the information I have provided useful, good luck.