First time using tampon!

Okay so I have tried on multiple occasions to use a tampon but I have yet to be successful. I'm 18 years old and it's embarrassing that I'm not able to use one. It's painful when I try and I don't think I've even gotten it partway into my vagina. I have used a mirror to look and see where it needs to go but my vagina just seems so small. I feel like this could be a problem in the future when it comes to sex, if I can't get a tampon in how am I supposed to get a penis? Any tips are helpful! Thanks