No STD would give you stomach pain or diarrhea. Also, washing with soap after doesn't do much to prevent STDs.
All that said, the only STDs that you could be at risk for are gonorrhea, syphilis and genital herpes type 1. You could also get NGU, which is an infection in your urethra, and can be caused by normal mouth bacteria. Your best plan is to go get tested for gonorrhea and NGU. It's just peeing in a cup.
The stomach pain and diarrhea could be from stress, but it could also be a stomach bug, food poisoning (depending on how bad it is), or any number of digestive issues. If it lingers much longer, get it checked.
Your chances of gonorrhea are pretty low - it's not often found in the throat, but NGU is pretty common.
You could also just be really anxious and hyper aware of every sensation that might be normal. Only testing will tell you for sure.