I had adenoids, my cheeks went inside due to open mouth breathing and my face got elongated: what do I do? (Photos)

Both implants and fillers in the cheeks can create good results for patients.  Both can build up the cheeks and create symmetry.  You must balance the pros and cons of each procedure and do what you feel is the best decision for you.
Fillers:
Pros: No downtime Reversible Quick
Cons: Temporary More expensive in long run
Implants Pros: Permanent Great for patients with poor bone structure Less expensive overtime
Negative: Risks associated with surgery Possible infection Downtime
I hope this helps.

 Hi, I have performed many facial shaping procedures using dermal fillers, silastic facial implants (cheek, chin, lips), liposuction and/or facelifts for over 30 years.  From the photos, your left cheeks is much more flat than the right side.  Having enlarged adenoids, as a child, has no effect on the formation of the cheeks (malar bone).  
 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.  When one or both cheeks are flat or concave in the front, cheek augmentation with precise placement of a dermal filler can  create full, round cheeks that will feminize the entire face.Hope this helps.