Do I have a weak chin, or does it appear like I have one because of my overbite and because of high body fat percentage?

From the side profile, there is a weak chin present, for which a chin implant can improve. Chin implants are manufactured in a large variety of sizes and shapes, and the correct shape can be discussed at the time of the examination and consultation. Chin implants are composed of solid silicone, and can be custom carved when necessary to match patient's unique anatomy. Placement of a chin implant is performed under local anesthesia through a small incision underneath the chin. For more information, diagrams of the  chin implants themselves and many before and after examples, please see link and the video below

  Hi, I have performed many facial shaping procedures, including Chin Augmentation with dermal fillers or silastic chin implants, for over 30 years.  From the photos, your chin is very weak.  When the chin is weak, this creates an imbalance making the nose appear larger, the mid face top heavy, the lower face looks short, de-emphasizes the lips and allows early formation of a "double chin".  
 Proper placement of a silastic chin implant adds forward projection to the chin thereby creating harmony and balance to the lower face.  Using the same incision, liposuction can be performed to reduce the fat and further shape the neck.  Excess skin, from below the chin, can also be removed through the same incision.  
 I have found that placement of a silastic chin implant, through a small curved incision under the chin (also allows excess skin removal) to be very safe, quick, highly effective and far less invasive than a sliding genioplasty (requires extensive tissue dissection, bone cuts and placement of metal screws and plates to secure the cut bone segments).  I perform chin implant surgery in 30 minutes or less, often using a local anesthetic alone.  In my opinion, you are a good candidate for chin implant surgery.  Hope this helps.