i need to know if im pregnant.

I'm 15. I was on brevicon birth control but I had to stop taking it last month because it was too strong for my body and I had two periods that month the second one the day I stopped taking the pills and I passed blood clots throughout the period. Ive had unprotected sex since then, more than once without being on birth control but my boyfriend pulled out every time.for the last 3 weeks or so, I've had severe head aches, stomach cramps, and nasuea which has gotten worse. Today, I'm three days late, going off the second period. And I had this weird sensation of being lightheaded and shakey. I feel like I'm having pre period symptoms but I'm not sure. Could I be pregnant? Please help.