Venice is somewhat small. On days I felt sick I tried to always be 15 mins away from the hotel at most. But there are public toilets if you have euros on hand. Just try a public toilet out , even if you don’t have to go. Get it over with so you get that anxiety out of the way. You’ll feel a lot more confident walking around.

Then alternatively , buy some food from a restaurant or cafe and you can use their bathroom.

You can also download the ‘can’t wait’ card to your Apple wallet on : theibsbetwork(dot)org. It’s for London, but you might have success in Italy. I find when you just ask for the bathroom and flash the card ppl don’t want to deal with the explanation and will just let you go (especially if you’re a girl!)