Yes, it's normal. The system for Prepaid SIM is that you can have up to 365 days of validity at any one time. You can extend it as the validity reduces. For example if eleven months left, you can use that number sequence to extend it back to a year for 3 baht.
Your issue is that you have allowed it to run down to just a few days and so have to keep applying it every month.
The advice to extend to the full year is good, but be aware that there is not a *934*360# option. It's seems someone just made that one up.
*934*180# for 15 baht *934*90# for 9 baht or *934*30# for 3 baht are the options available.
Alternatively, if you have TRUE Points, 30 of them can be exchanged for 365 days of SIM validity. 10 point for 120 days or 3 points for 30days.