Whoever goes to HEAVEN, expects to meet angels, whoever goes to HELL, expects fire, but.......whoever goes to PATTAYA expects A LOT OF FUN. EVERYWHERE!
I was also not married to the child's mother when my daughter was born in Bangkok. I just made sure that the hospital included me as the father on the birth certificate. Afterwards I had to confirm paternity at my local embassy in Bkk. With all these documents I then went to the Thai registry office (Amphur). No problem! No lawyer needed. My daughter got both nationalities immediately.
Check if your Thai driver's license has an expiration date. If so, then you can only use it for one more year. After that you have to make it completely new.