Sorry, I have never been to Thailand and my recent attempt to get an overview of Thai prepaid SIM packages for a friend who flew to Thailand was unsuccessful as most operators' websites are only partly translated into English.
I only found out that from AIS there is a product called "GSM Advance" and another one called "1-2-Call" but I don't know which of them is prepaid, what the SIM card costs and where you can buy it.
I also found this overview of data packages, of which some are only available to "GSM Advance" customers while others are only available with the "1-2-Call" tariff:
??????? Internet Edge, 3G ??? Wifi ?????????? | AIS Mobile Internet
Also it seems like these packages can only be ordered by USSD codes, which you can only enter with a phone but not with your Huawei pocket router.
Finally these are the APN settings for AIS:
APN: internet
username: ais
password: ais
I gave you a link for a tutorial
here only three months ago.