Can’t use tampons??

Okay so I am almost 18 and I can’t use tampons. It’s like they literally won’t go up! I’ve tried the smallest sizes and it’s like it hits a brick wall. I know I am putting them in right, I’ve had several friends double check (haha I know) and they said it’s the weirdest thing. Anybody else have this issue?? I’m scheduling an appointment with my doctor soon. Pads are too much of a hassle.🤦🏼‍♀️