Im male, 26 yrs. for past 4 days i have been getting headache concentrated to left side. when i bend down the pain gets worse. what could be the cause?

Headaches: Left sided headaches that change with bending or stooping are difficult to define without further clinical information and an examination. Most often they are due to a neck strain and muscle spasm. Because the headaches have been ongoing for four days the best course of action is to see a neurologist/neurosurgeon who can define the type of headache and prescribe a treatment to eliminate them.