help me please

why can't i get a tampon in? i'm 16, and have had my period for almost 3 years now. i've worn pads this whole time, but recently i've wanted to make the switch to tampons seeing as i'm growing older and more mature. for my past three or so periods i've found the time late at night to sit down in front of a mirror and try and get a tampon in. however, it just won't go in. i tried again tonight and thought it would be easier seeing as my flow is heavy right now and the blood makes for good lubricant. i was able to get the tampon partially in, but not fully. i don't know why it won't go in, what am i doing wrong? i've tried many angles and positions (standing, sitting, laying, squatting, etc) but it just WONT go in. is there something wrong with me? with my vagina? i don't understand and it's so frustrating that i've been crying for 30 minutes straight... i need help. somebody please ):