When in Thailand go to a local, private clinic. Ask if the Doctor will sign your medical form for a work permit.
Many will do so without even taking any tests. Some will ask to see you, check you are breathing and have a heart beat and then sign your form.
If the first one you go to says they must take tests, move on to the next one. I had work permits, teaching, for 21 consecutive years. Only once did the doctor even bother to check my chest with a Stethoscope and take my blood pressure.
At one clinic I used to go to the doctor would sign a bunch of forms and leave them with a receptionist. Hand over passport and 100 baht and she would complete them. Half the time the doctor was not even there.