Tampon struggles

Why do I sometimes have trouble getting a tampon in? Like sometimes it goes in perfectly and I can't feel it. But sometimes it's like it can't go in far enough and it feels like it's coming out and I leak a lot, I wear a pad all the time just incase. Is there anything I cha do to make it go in perfectly every time? It's just really uncomfortable and I get really bad cramps in my back because of it? I don't want to stop using tanpons because they're much easier but only when the go in properly. Sometimes it really helmets and is really sore and stings when j try and put one in? Anyone had this or have any tips on how to stop it from happening? Thank you xx