right implant is higher and larger - what can it be?

Hi. You may have developed a (late) fluid collection around the implant called a seroma. This can be established by a sonar / ultrasound. There are many causes of fluid collection around implants and it is important to find out more about it, so my suggestion is to see your plastic surgeon as soon as logistically possible so that further review can take place. If it is fluid, then some of that fluid will be drained off for lab analysis.

Hi and welcome to our forum!
From your photo, the right breast appears spherical and is riding quite high.
If the change was gradual and if the breast is firm, this could represent a capsular contracture.
Following the procedure of saline or silicone augmentation mammoplasty, the surgical wounds seal and undergo the healing process. This occurs in the underlying soft tissues as well. The silicone polymer making up the shell of the breast implant is biologically inert, and as such, the body creates a thin filmy internal scar which surrounds the implant, holding it in its position. Thus, all breast implant procedures involve the development of a thin capsule. This becomes problematic only if the scar shrinks substantially around the implant, thus causing a capsular contracture. Manufacturer publications state that this will occur in approximately 10% of all augmentation procedures.
Generally, capsular contracture only needs to be addressed if the patient experiences discomfort or if the implant becomes displaced, affecting the aesthetic outcome.
The precise cause of capsular contracture is unknown but is unique amongst individuals and their individual immune response to the placement of a foreign body. Its incidence is increased in the presence of infection. Capsular contracture is not predictable nor a by-product of surgical quality. It is highly recommended patients learn and follow a massage routine that will dramatically reduce the incidence of contracture. While postoperative massage will help prevent contracture, there exists the possibility that the degree of contracture may require an outpatient procedure to remove the scar tissue.

The apparent increase in size may be artifactual, but suggests an internal collection of fluid, the nature of which is unknown.
I strongly recommend an urgent visit to your plastic surgeon for evaluation and treatment.
Best wishes...