Why have my lips gotten bigger without any interventions 2 years after fat transfer???

What you are describing is very normal.  The fat that we transfer is living tissue.  If it survives the transfer process and "takes," it will act like fat in other parts of your body.  That is, if you gain weight, your body fat (including the fat that was transferred) will plump up.  If you lose weight, your body fat will, shrink.  The greater the weight change, the greater the difference you will see in the fat that was transferred.  I hope that helps.  Best wishes.

Fat injections can change with weight loss and gain.  If you are concerned with the look please see a cosmetic dermatologist or plastic surgeon who can evaluate your lips and consider the best options for treatment. Dr. Emer.

The change in size of your lips is most likely associated with your weight gain.  If the fat was transferred from your abdomen your lips can enlarge as your abdomen enlarges with weight gain.  Other factors can be the use of hormone replacement therapy or oral birth control which may lead to weight gain. In any case, over time there does tend to be some loss of fat cell volume in lips that have been fat-grafted so the problem may take care of itself without treatment.  Hope this helps.