Can I perform a visa run to Myanmar after multiple border crossings into Thailand?

Looking at her profile, the OP appears to be Spanish.

I re-read your post, and this stood out to me:

"I flew into Bkk on a connecting flight to Cambodia, but I got the visa on arrival I didnt use."

I can't imagine any way a person can get a "visa on arrival" (OR a visa exempt) without stamping out of Thailand. I imagine if you somehow stamp into Thailand, then turn around and return to Cambodia, etc. without stamping out, you would have entered on overstay after 15 or 30 days. It sounds like that didn't happen. I would check your passport and confirm there is a triangle departure stamp.

IF you are from a visa exempt country, AND you flew in by air, that did not count against you two visa exempts by land.

If you are from a visa on arrival country, then you qualify for unlimited visa on arrivals, BUT I don't think you can use the Kanchanburi/ Myanmar border.

See: %20on%20Arrival/VOA.pdf

"visa on arrival I didnt use"

What is a "visa on arrival" and how did you get one without using it? How many days was this "visa on arrival" valid for?

What's your country of passport?

If you came into Thailand passing the Malaysian land border and got a 30 day stamp in your passport you can, depending on country of origin of passport apply at the local immigration office for a 30 day Extension of Stay or make another border run for a new 30 day entry.

But for 54 countries these entries without visa are limited to twice a calendar year, this is the list of the countries who are limited:

What is the country of origin of your passport? You tel about Visa on Arrival this is only for 15 days and available for 21 countries.

You flew into BKK, got a visa on arrival but did not use it, I guess you passed Immigration so the stamp is used.

If you flew in that does not constitute a land border crossing