Hi and welcome to the forum! I am glad that I can help you.
You like to know what is the reason for the pain in your head and eyes.
Pain in the head can appear in one of the following situations: migraines, brain tumors, increased blood pressure, increased cerebrospinal pressure, nervousness due to stress and vision disorder. Losing weight fast more than three stones (20 kilograms) in one to two months time is suspect for any malignant process with in the body.
Given the data that you described it is likely that you may experience headache due to increased blood pressure or headache due to vision disorder. You may consider seeing your doctor to check upon your blood pressure. You may also see ophthalmologist to check upon your vision. You may consider doing a scan of your sinuses to rule out sinusitis. Finally, you may consider seeing neurologist is the headache is constant, pulsating and increases due to light and noise.
Please keep in mind that I am trying to provide you with medical information here. I am not able to give you medical advice online. Please contact your doctor or a qualified healthcare provider such as ophthalmologist and neurologist for further advice, diagnosis and treatment options.