Immigration stopped and questioned me. pls advice


In 2016 I spent 11 months in Thailand and always stayed legally with a tourist visa that I was renewing every 3 months at different embassies in Lao.

After working in Vietnam for 7 months I flew back to TH today and as the immigration officer was turning the pages of my passport back and forth for 5min then said: "computer show up".

Another officer with better english showed up and asked to follow her then said:
"no work in your country?" "how long you stay"
"why in TH so long? u can only stay 90 days in a year".

I replied that I have a girlfriend here and I am working on Vietnam and I will be staying only 4 days.
They then stamped my 30 days pass.
And they said that This questioning may happen when I re enter.

I need to ask you please if the law has changed because I was in shock today; why giving me the
3 months tourist visa on Lao and then questioning me later??

I am now worried that I will have a lifetime trouble when I reenter Thailand. And I have a
girlfriend here.
What options do I have to avoid this harassment? do I need to Apply for a visa or change passport?

thanks a lot

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