Based on your photo, you should be able to get moderate correction with Botox. This area tends to do better with consistent treatments every 3 to 4 months.
Based on your photos, I do not see any lines/wrinkling. If you have an area that you would like corrected, an experienced injector could advise you at a consultation.
Botox is measured by units rather than cc's. Generally, "sprinkling" or multiple injections of smaller doses are used to provide correction for a variety of reasons including those who want to retain movement, areas that are lower on the forehead, etc.
Based on your picture, it doesn't appear that Botox would help correct this. While Botox has helped some with migraines, your description doesn't sound like a migraine but an ongoing, consistent pain. Definitely see your family physician for recommendations.
The forehead is very receptive to Botox treatments and typically excellent results can be seen in this area. Start with your provider's initial recommendation for dosage and recheck in 2 - 3 weeks. It is possible you may need a touch up or change in dosage at your next visit for optimal individual results.