A video or a picture of you lunging your horse would help, but, as far as I can imagine, what's happening when you try to do that - have you tried putting the pressure of your body language at the horse's forequarters, and, when he's on the circle, right behind his back, if needed, by swinging the whip - but not with the intention to touch him with the whip, albeit the ground just behind his tail, as if you were saying "I want that ground you're standing on, MOVE!". If he doesn't move, your whip will land on his tail/hind legs, and he will learn quickly, what is to be done to avoid that. Also, don't turn against his hindquarters, when trying to send him on a circle, because with this movement you just swing his hind end off the circle, and his head against you - imagine as if you were swinging a gate open away from you.
And, as soon as he reacts to the amount of pressure you've used, take it off immediately and praise him. Start with the little details and go slowly, there is no need of making to lunge him like a pro in the first day.
I have come a long way, to surrender my shadow to the shadow of my horse.