I've been working on a mod -- pretty cut and dry, I created a few new potions and a few new lines of dialogue. I have not changed anything else (to my knowledge). When I tested the mod, I came up with an interesting problem. In front of many services and the "OK" button, a lowercase "s" appears. Aside from being an aesthetic bother, it messes up quite a bit of dialogue and the price of services increase by 1000%. I have no clue how adding a few potions and lines of dialogue could have caused this. Could anybody be of help?

Generally that means you have a case of the "evil" GMSTs and need to clean your mod. tes3cmd is good, I think you can do it with wrye Mash but I don't use that myself, and also testool, but that can be a bit dicey.

Oh is that all? Good. I've tweaked mods before but never created them. If anybody else has an idea of what else it may be, please say so.

As neildarkstar said.
Some info on http://www.yacoby.net/es/forum/12/3710281144934700.html (also http://www.uesp.net/wiki/Tes3Mod:GMST_Contamination ).
Also, see http://wryemusings.com/GMST%20Vaccine.html info and get it.
Some more info on possible http://abot-morrowind.tk/index.php?Itemid=36&option=search&q=gmst