if you've never used a tampon before, it can definitely be a jarring / nerve-wracking experience, but rest assured, it doesn't have to be. unless there is an underlying health condition, it is not harmful in any way to use a tampon - vaginas are, by design, suited to withstand things going in and out. i think it's great you've sought different solutions to avoid tampon usage if it makes you uncomfortable, but sometimes (like this situation) you gotta do what you gotta do. it does sound a bit that psychological factors are causing / contributing to the degree of discomfort that is happening when you try inserting a tampon. it helps some people to take some deep breaths and relax their muscles - tension increases pain, and inserting tampons when you're not actually bleeding can hurt too. i'd recommend talking to your doctor about this pain, because it does seem much more extreme than most experience, so it's important to rule out any underlying conditions that could be causing this. alternatively (though still bring this up with your doctor), you could talk to your swimming instructor and tell them you can't swim that day. most people will get it and make arrangements around your predicament. hope this helps!