This had never been a problem until around an hour ago. A friend texted me and it showed up on all 3 other iPhones my family has (we all use the same Apple ID). I tried turning my phone off and on, then turning off iMessage, then sending it through my own email (which didn't work, because her texts just sent to everyone but me). This has never happened before, please help!
On your own iPhone, go to Settings > Messages > Receive At. Tap Caller ID and make sure it is set to your phone number.
Optionally, on the other iPhones, go to Settings > Messages > Receive At. Tap your Apple ID at the top of the screen and choose Sign Out.