Only Lasted 4 Weeks

My doctor said that this product would last 6-12 months, sometimes longer. I'm not sure who it lasts thing long on.... My lips were beautiful and full and now they are small again. The filler only lasted about 4 weeks. At first I noticed it going down and down and down. When I woke up this morning my upper lip was the same size it was before the juvederm. I'm still noticing a little larger pout on the bottom, but nothing like right after I got the juvederm. I'm very disappointed because I thought this product would last at least 6 months. It was great until it went away. I can't afford to have it done again at 500. Has anyone else had this happen to them?