It seems from the history that you had a small bump on the forehead and the indentation can be because of healing of that lesion. Since you had headache even before the lesion,it may not be a cause for your headache.
Hence you need evaluation for headache to find out the underlying cause and treatment accordingly.
The common causes need to be ruled out are primary headaches
, eye problems like refractive errors and ENT diseases like sinusitis
Hence I advice you to consult your doctor for examination and treatment accordingly.