You coming here with a Swedish passport gives you a Visa Exemption of 30 days.
You do not pay for anything on arrival, but you will need to show proof of outbound flight from Thailand within 30 days.
You can extend these 30 days at a Immigration office in Thailand, 1900 for another 30 days. But after this, you need to leave.
If you want 3 months in Thailand, apply for a Tourist Visa ( or Non O for Retirement if you are 50+ and fill the other requirements ) BEFORE you come here.
A normal Tourist Visa gives you 60 days when you arrive, and can be extended with another 30 days for a total of 90 days.