TMJ causing headaches --- Anyone?

I have had a rehabilitating headache for over 12 years now. I've been to three university's neurologists and scores of others The latest diagnosis is chronic migraine, Doctors tell me that i have give the drugs and therapies more time to give me relief. I am scheduled for more Botox in October. Last May i had a series of MRIs and although no doctor picked up on this, i saw in the report "Severe TMJ left side." My research shows that TMJ can cause headaches. Paying attention to that possibility, i notice that my left side jaw clicks or pops with almost every chew. Even opening my mouth to insert a toothbrush causes a pop. One must eat and doing that chewing happens several times a day. This may account to the fact that the headaches are constant and never stop. I am now wearing a dental appliance which my dentist says should help. I also am into physical therapy for TMJ. No help yet. Migraine Caps that stay in the freezer until i wear one is the only significant relief i have found. The pain returns upon removal. Have any of you encountered headaches attributable to TMJ? What relief have you found?