You may be able to find it where tropical fish are sold as far as over the counter goes. Branded as "Heximet" or similer as I recall. Metronidozole is a good antibacterial agent in the anaerobic side of things; i.e. In a lack of oxygen. Sold in sugar laced nasty tasting liquid in third world for such things as Montezuma's revenge. Has been years since I have had occasion to use it. You can google something like "Flagyl dose for my Cornsnake" or something along those lines for peoples thoughts on milligram doses. It is regarded as having a wide range of safety. While you're at it try a very small, easy to digest food item like a fuzzy rat and see if that stays down. Less hair to deal with.