I'm a little desperate for sex.?

Yes I do mean moms plural. Me and my girlfriend have been together for 15 months on valentines day, and ever since we were 3 months in we were having sex and we told our parents a few weeks later. Since then they have gone out of their way to make sure that me and her are never together in a place that having sex is ok. We are both 18 and in high school and we have only had sex maybe a dozen times since her moms learned and it has been 4 months since we last had sex. Neither of us are willing to move out because we are financially unable. Me and her have had arguments about how we never do anything even when we can find a few minutes to be alone, and we both understand the reasons, and even the fact that they are good ones. Anybody have any kind of realistic advice? Warning: stupid comments will be flagged