You're certainly not being ridiculous; it can be majorly stressful when our bodies don't do what we think they should. But, it may help to know that you're far from the only person who's had an issue like this. In fact, we have an entire advice column dedicated to this issue, including ideas for what to try to resolve it: https://www.scarleteen.com/article/advi ... hould_i_do
. That piece goes into more detail, but I want to highlight that fact when we're tense, it gets extra-hard to insert things into the vaginal canal. If you have a history of trying to insert a tampon and it being painful, then part of what may be going on is that when you try the next time, your body remembers and goes "oh no, that hurt last time, I'm going to get tense."
Just to check, have you ever seen an OB-GYN? If so, did you mention this issue to them?