as Lynnette advised but make sure if questioned you are a tourist and have baht in you pocket have a different address when you enter. But soon you will need a long Visa
ok YOUR ENTERING ON NO VISA. That's called VISA EXEMPT They are questioning on your purpose here. Always have baht in your pocket always tell them you are a tourist. Change your place to stay as if you show the same residence they think you have a gf
Never tell them you have a Thai girlfriend. Space your trips into here as too many and the IO may deny you. Otherwise go for a long term visa.