Why cant i fit a small tampon in

So ever since I first got my period around 12 I’ve been trying to put in tampons and I just cannot, it’s like hitting a wall. I’m 19 now and I finally started to see what’s up and my hymen covers my entire entrance? But I know there’s an opening somewhere bc my period flow is always heavy (and started taking birth control to stop my period and now I only have it once every 3 months) anyways I’ve tried stretching it out but it hurts and I’m always tense which I think may be the problem? I also just have severe anxiety in general and I’m scared of hurting myself if i try too hard even though the vagina is literally made to pop out a BABY

Has anyone else experienced having a lot of anxiety with this? Or does anyone have any advice to relax?