So you have no symptoms on your penis, it doesn't hurt or itch or anything, you have had pain that you think might be kidney stones (have you had those before?), and a blood blister in your mouth after eating a too-hot and hard pretzel, and have had some loose stools.
I'm not sure why you would connect all that with an std, but if you are concerned, get tested.
Have you given oral sex to anyone? That's the only way any mouth symptoms would be connected to an std - you can't get an std in your mouth if you don't give someone oral sex.
I'd also be concerned with what you think might be kidney stones - you should get that checked out, too.
Aj
PS. this was one time with each of the 6 people.