Indent and line under chin 5 months post chin lipo (Photo)

Based off your photos - the muscle bellies you are seeing are the digastrics and platysma. Liposuction can not remove muscle and because you had chin lipo, the fat that was there covering these muscles are now thinned out and much less, you see the muscles more. Without seeing a before photo or examining you, those muscles were probably already pretty prominent even prior to the lipo (being that you are young also). Not many options you can do to make that less noticeable but try speaking to your surgeon to see if there are any other options.

From the pictures, it appears that the liposuction of your neck was slightly overdone, and now the borders of the platysma muscle are exposed. This is resulting in the lines or indent that you are seeing. This could be corrected with a deep plain neck lift, where the platysma bands would be addressed. 

What you are seeing is the outline of your platysma muscle. This can become quite noticeable after overaggressive liposuction. The superficial fat of the neck needs to protect and "act as a blanket" to cover the deeper structures. I would recommend an open submental incision neck lift to repair this problem. I recommend seeing a plastic surgeon who has completed at least 6 years of plastic surgery training (ideally 7 if an aesthetic fellowship was completed).