My chin is weak and my cheeks are chubby.

Without an exam your question cannot be answered.  You will need to see an Oral/Maxillofacial surgeon to see if othognathic surgery, genioplastyor using an implant is best for your specific case. It should be noted that patients with severely weak jaws or abnormally functioning jaws maybe better treated with other facial surgery (orthognathic surgery), although a chin augmentation may be an option at a later time. These patients should seek the advice of a plastic surgeon to determine which course is right for them. Here is some information to help you make thisdecision: Candidates for Chin Augmentation - Patients whose chin profiles are weak but have normally functioning jaws are candidates for Chin Augmentation. Many of these candidates have used injectable fillersin the past to strengthen the protrusion of their chins, but are looking for a permanent solution. If you are one of these patients, thenyou are a likely candidate for chin augmentation

And full set of facial photographs  are required to make a determination about being a candidate for surgical chin implant.  Chin implants are placed for patients who have a weak and  recessive chin profile.  For more information and many before and after examples,  please see the link and the video below

 Hi, I have performed many facial shaping procedures using dermal fillers, silastic facial implants for the cheeks, chin and lips, liposuction and/or facelifts for over 30 years.  It appears that you are a male from the information provided (if you are female, see the information at the end of this post).  Following my beauty principles, men look chiseled and handsome with angularity in the cheeks, chin and mandibular angles.  Non smiling photos of your face from the front and side would help in the evaluation.  In general, the following procedures would create a more ruggedly handsome face.
Cheek augmentation with silastic cheek implants (permanent enhancement) or precise placement of a dermal filler (temporary enhancement) to add angularity to the cheeks and mid face.  Liposuction can be combined to reduce any excess fat to further shape the cheeks and face.
Chin augmentation, using a chin implant, to add projection to the chin creating harmony and balance to the lower face.  I have performed many facial shaping procedures, including Chin Augmentation with dermal fillers or silastic chin implants, for over 30 years.  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.  
Augmentation of the mandibular angles using a dermal filler (jaw implants have too many unwanted side effects IMHO) to add volume, angularity and flare to the jaw line.
 Following my beauty principles, women look the most feminine, youthful and attractive with heart shaped faces.  Heart shaped faces have cheeks that are full and round in the front.  Cheek augmentation with a dermal filler or using cheek implants for a permanent enhancement will create full, round cheeks that will feminize the entire face.
There are many faces that have excess fat over the cheek area which hides the "true" shape of the cheeks below.  In addition to obstructing the cheek shape, this excess fat will sag prematurely as it is pulled by gravity at an accelerated rate versus a face without excess fat in the mid face.  Removal of the excess fat, with liposuction, is key when properly shaping the cheeks with cheek implants.  I have used this in combination with cheek implant surgery for 30 years.  In my experience these procedures when combined in a face with excess fat in the mid face are extremely safe, effective and reliable in the aesthetic results they produce.
Hope this helps.