I have noticed a good size lump in my left buttock after BBL. What could this be? Opinions? (photo)

I had BBL surgery in aug 2018, now 5 months later this spot has surfaced even more. The area was tender the whole recovery, and now I see why. The lump is irritating and gets really sore when I sit or lay on it for too long. I went back to my surgeon and he told me to take advil for pain and to apply a warm compress on it, neither of which I think will resolve this issue. I just want some more opinions on what this could be or what caused it. Thank you.