contraception?

Okay well I lost my voice about 2 months ago with a girl I really I love and yeh sh, and she'd on the pill anyway for her periods but she forgets to take it sometimes and she's 15 I'm 18 so a kid wouldn't be the best and her dad would kill me if he found out we were even having sex, so I need advice on contraception methods, the rod isn't the best idea cause she mostly wears sleeveless tops and her parents would put 2 and 2 together, and condoms art my thing, I think I'm allergic and it's so much better without and it kills the moment when I get up to go into my drawer for them, advice?