What is going on with my weak, undefined neck/jaw? (photos)

Please help, this is making me so selfconcious. I really want to get treatment to fix my horrible weak jaw/undefined neck but I don't know what the issue is. A chin implant has been suggested previously however I have a long chin so I don't think this is the answer. I have a narrow face that looks okay from the front apart from long/witches chin. I'm not over weight so don't think this is the solution. I don't understand why I'm missing that angle under my chin & it's making me miserable.