He looks very uncomfortable.. he's very hollow.. it has to be due to pain or a threat of pain. Some horses are ridden so poorly that they are scared to be ridden and take a long time to get to relax and enjoy the ride. My horse bolted.. he went from pasture puff to being schooled daily (just walk trot) and he was very un trusting under saddle on top of the fact he carried himself like a giraffe and hollow like your horse seems to be. You look fine.. he looks over phased in the lunging photo with the halter on underneath the bridle.. he looks confused like he doesn't know who to listen to.
I definitely agree with everyone else.. you need to get him solid and trusting on the ground. Work out these lunging issues. If you need help with him because he's strong or whatnot, definitely bring a trainer into the mix and get help from them! Focus on halting when immediately asked, and standing still and relaxing. Work on teaching him to lower his head on the ground and release his jaw by sticking a finger in the corner of his mouth (like you do to bridle him.) My horse was helped so much by me taking time to make sure he was relaxed. Also, take things slow.. and always end on a good note :)
I wish you only the best of luck! You'll get through this!