Zofran and bleeding

Why can't pregnancy just go smoothly?! My doctor prescribed me zofran because I have been so nauseous and I took my first dose around 5pm. Woke up 45 minutes ago after being asleep for a few hours and I had heavy bleeding. I freaked out and called the after hours number and they want me to call the office in the morning and go in. I haven't had any clots or cramps and Ive had some additional bleeding but I can't help but fear the worst. I am 13w3d....thought we were just about in the clear! Has anyone had this happen to them???