@Richard ******
, sorry, for my curt, terse and abrupt manner :O
yep, you're right,
You are now here on a 90 day Non-B stamp IF you are going to leave and come back within those 90 days you need to BUY a re-entry permit (BUT that re-entry permit will only be valid for those 90 days) :(
You need to get the documentation together so you can apply for a yearly extension of stay at the immigration office when you have 30 days or less left on your current stamp (bangkok is 45 days or less but most offices are 30 or less).
Once you get the year extension you can buy a re-entry permit that will keep that extension stamp "alive" so you can exit/re-enter the country and get stamped in until it's expiration date. (The re-entry permit you get AFTER you get your year extension will be valid for the whole year :) )