why do I bleed every time after sex??

Okay so not every time. I'm 17, had sex 4 times now in the past 2 months. The first time I didn't bleed, but also proabably bc he had whiskey dick so it didn't really work, ya know? 2nd time I spotted after it. 3rd time no blood. 4th time, blood. Why? Is it possible to "pop your cherry" more than once? What's the deal