Heavy feeling in forehead 1 year after Botox

Hello all, a year ao todayI had 10 units of botox placed in the upper quadrant of my forehead done by a board certified dermatologist. Two injection sites were utilized during the procedure, a few inches above my brow arch for reference. This was my first time recieving botox at age 28. I was doing it for 'prevention' rather than to treat any existing fine lines (i didn't have any really. A year later i still have extreme heaviness in the left side of my forehead. Why?