"when i mix , i am prety much dead center of the room" -
Take your entire mix station, and however you have to do it, get your head out of your (ahem) center...
By this, I mean move forward or back, up or down (stay centered left-to-right)
And while you're at it, measure and make sure that your speakers are NOT sitting at 1/4 of the long dimension away from the wall in front of you. Even 6-8" can make a noticeable difference. By that, I mean that if you are facing the long way in the room, your speakers should NOT be where their baffles are 27" from the front wall, or they will be "sucked dry" of bass that coincides with the 9 foot dimension of your room - If you have them at that distance AND your head is centered front to back, also maybe top to bottom centered, then you are not hearing more than maybe 10-20% of the bass your speakers are putting out, if even that much.
You still need to do the treatment mentioned by John, but move things around if you can and see what a difference it makes... Steve