I don't know, given everything you have tried it might be important to re-establish ground rules. Round pen, not allowing the horse to do his thing until you say so. That will establish your dominance.

Secondly I would never use a bit on a green horse, I always started a horse with a bosal. He may be head shy because of the soring caused by the bit the trainer was using. Keep in mind, for 90 days this animal was being trained by someone who, from all appearances, was abusing your animal. You have to gain his trust all over, and I would suggest doing that by not using a bit (what your horse probably views now as a torture device). You can go back to a bit later in conjunction with the bosal.

Have you lunged him saddled and bridled? Does he toss his head then?

Is there someone that can pony you from their horse so you can concentrate on riding without a bridle?

Personally I would not give up so easily. When I was young there was an Arabian Stallion that I worked with. He bit, struck out with his forelegs and was basically a brat. So much so, that I refused to breed my mare to him. I could have kicked myself! He went on to become the Intl. Arabian Stockhorse Champion in 1975... I could have had FREE breeding (a true V-8 Moment).

I became very adept at thinking creatively with him. I would watch him like a hawk and when he went to bite me would calmly grab his nose and twitch him. I wouldn't do it hard, but I wouldn't let go until he settled down. If he went to strike out with fore leg, I would make sure it met squarely with the TIP of my cowboy boots. He finally figured out I was smarter than him and stopped playing one upsmanship with me. But let me tell you, it was a rough 6 months to a year!

Arabs are a high strung breed and very intelligent. That also means they excel in getting into trouble! Also, understand that Arabs are slower to mature than breeds like quarter horses and thoroughbreds. For an Arab, 4 is a teen, not fully mature. And just like human teens, they manage to get into a lot of trouble at that age. Have patience just a little longer. If you use a trainer, be sure to use one where YOU are involved in the process!

Hope this is helpful, and I wish you the best of luck.