It sounds like this baby doesn't know how to move off of pressure, has no concept of you and your space and so I would recommend for a bit, the only work you do with him on a line is just having him move forward, backward, step his shoulder over away from you , and yield his hind quarters away from you.
These are rock bottom basics. I like to work with a rope halter and a heavy cotton lead line of at least 14 feet in length, but even 12 feet will do.
And, teaching him to lead respectfully, i.e. not overrun you, will be your next step.
If you free lunge him for exersize, then until her understands these basics, I would either not lunge him at all, or keep free lungingin the round pen as basically "play" or just you pushing him away and forward using your body.
REally, tho, I'd take some time and work on these very basic things.
Before trying to lunge him on a lungeline.