Why do tampons hurt??

So I’m 23 and have used pads for the entirety of my lady hood 😜❤️💃🏼 I bought a diva cup a few years ago and only managed to use it once. Hurt like a mofo. I’ve tried tampons before but they hurt too. I was on a flight yesterday and thought it would be wise to buy some tampons in case I were brave enough to try using one, for cleanliness purposes. On my layover I decided to try, and oh my god it hurt so bad. I could hardly walk, and sitting down hurt SO bad. I had to take it out like 20 minutes later. Why does this happen?? It’s not that a tampon doesn’t fit me. It’s literally like that time of month my insides reject everything lol. Also anytime I am sitting up having sex I am in that same pain. It’s like as soon as I am upright the piercing pain happens, same as when I put a tamp in. Is my cervix weirdly set or something what is going on?? Why does anything up there hurt when I’m upright?