What's wrong with my jaw/ neck? Would Botox help make my jawline not "droop" like this? (Photo)

This is not something age or weight related since I've always had this and it doesn't change depending on my weight. When I touch the area it feels tense which makes me think it's muscle related and it also feels like it's "pulling down". Could this be due to tense jaw or neck muscles and would botox in this area make my jawline not "droop" like this? It's like the underside of my chin is bulging out.