Without photos it is hard to advise you on what's going on. With your short description it could be capsular contracture. The hallmark of contracture is one breast becoming firm and moving up towards your collarbone causing the nipple to rotate downward and can even be painful. Capsular Contracture is not well understood, and a single cause has not been identified. Leading theories include: subclinical venous bleed, low level bacterial contamination and/or biofilm, lint contamination from sterile drapes and genetic predisposition. Since the cause is unknown, treatment typically involves addressing all possible causes. There are four grades of contracture. Grade I is normal, looks good and feels soft and does not require treatment. Grade II feels firm but otherwise looks good. Grade III feels firm and looks distorted at rest. Grade IV feels firm, looks distorted at rest and is painful. Aggressive massage +/- Leukotriene Inhibitors can improve/soften Grade II contracture but in my experience rarely improve the superior malposition present in Grade III and Grade IV contracture. These respond best to surgical revision/capsulectomy and implant exchange. Best to return to your operating surgeon to assess what's going on in person. Best of Luck.
Since it has been three years since surgery, you will probably need surgery to lower the implants. I would suggest discussing all your concerns with your surgeon.