What would make a horse shake their head side to side only at a lope?? Perfect at a trot but the minute start loping she shakes her head side to side and hops around like a jack a$$ for a few strides. Then go a few strides and shake head again. I've had her treated for ticks in her ears, teeth done, chiro,etc. Is it just a habit?!! Is she just a witchy mare?  Please help before I pull my hair out!!

Sore front feet and kissing spine are two things that come to mind immediately.

Head shaker syndrome. 

Omg I just googled this. It also said they sneeze a lot and she does!! She sneezes and shakes her head constantly at a lope!

Have you had her TMJ checked? Sometimes getting a horses teeth floated can cause issues with the TMJ. Do you have any videos of you riding and her shaking her head?

I don't but I will make one tomorrow!! I've been riding her everyday thinking she just needs more wet saddle blankets.  I just don't want to give up on her but I'm so frustrated at this point. 

I would also take xrays of the face and neck to see if there are any fractures in the neck or sinus area. 

It's been a while but seems I remember headshakers was a sensitivity to light on a certain part of the nose!??  I know people have made face covers that have really helped as they rode. There is a nerve involved I believe. 

If you can find this video, its Horse Massage: Releasting Tension in the TMJ using the Masterson method. Its really interesting.

I think it's the trigeminal nerve. . . 

From what you posted it doesn't sound like a head shaker to me. I had a head shaker and she couldn't control it. She did it all the time whether she was free in her own, tied up or being ridden. She truly could not control it. Another sign of it is a very dramatic upward jolting motion like they got a bee up their nostril. Again they do this randomly and at all different times--and it is a very violent and sudden movement. I don't think it would hurt to have your vet consider head shakers but her symptoms just sound like it's something else to me. 

Yes, Masterson Method...videos on You Tube have a very easy method to help the horse release tension in the TMJ area. Also Vicki Wilson on Facebook, just posted a good  video showing TMJ release method, that should help, if that is what is wrong with your horse....not sure if that would help with Head Shaking Syndrome though. She has other videos as well, how to massage their foreheads, poll area.