Hi there-
In the Brazilian Butt Lift technique, fat is removed from one area of the body and grafted into the buttocks to improve shape and projection. This fat is dependent on the diffusion of nutrients from the surrounding tissues for the time it takes for new blood vessels to form that will nourish the new tissue in the long term.
If some of the grafted fat cells don't get enough blood flow, they will either be absorbed by the body (which should be expected to some extent with this technique), or will become a firm mass called fat necrosis. It sounds like this is what you have experienced (although of course there is no way to know for sure without an examination).
If this is in fact fat necrosis, there are several options available to you- you should discuss these with your surgeon, but generally the area will soften over time (although it sometimes takes more than a few months).
Talk to your surgeon about the options- usually time takes care of the problem, but understanding the problem and the options will probably make you feel a lot better.
Contact the doctor
