IDP is issued in your home country based on your driver’s license from your country. Usually an IDP is issued for one year and if stopped by police you need to show your IDP along with your valid license from your country which issued your o
you have a few choices. Go to Thai immigration and apply for an extension. Or go to a visa agent and they will do for you. You can do a border bounce which will take longer than getting an extension at immigration. Or you do nothing and leave Thailand after your 35 days. You will be fined for each overstay and you will have an overstay stamp in your passport. This is not good if you plan to return to Thailand in the future
A multi entry is a stamp you get in your passport when you have a retirement visa. The cost is 3800 THB and is valid as long a your retirement visa is valid. You can also purchase a single entry which is 1000 THB. Both you purchase at immigration.