The opium tincture (laudanum) is available by presc only and is for extreme diarrhea (which you and I experience). My dosage is .06 millilitir 4 times daily in liquid form. This is less than 1/4 tsp. Since it is a narcotic I limit the usage -- normally twice a day. One side effect can be dizziness and being light-headed, something you would not want if you resume teaching. In the meantime I hope this helps.
And you will learn to scope out the bathrooms when you are able to go out and about -- the first thing I do when shopping. Also wearing plenty of protection and carrying an extra change of clothes is a must.
And one other tip I might offer for the burning is to finish wiping yourself with liquid Maalox. Externally it can have a cooling effect.
J'nette