Menstrual blood isn't just blood. It's uterine tissue (endometrium) and mucus, too. That's the chunky stuff. It's normal. when a girl goes on the Pill, that causes changes to the way she menstruates, so for the first few cycles or so, her period may look different to her.

As for unprotected sex, STDs are always a concern for couples, especially if they haven't been monogamous for over a year. That's pretty common for teens and young adults, which is why it's just so freakin' important for all of us to get tested regularly for STDs. Make it a couples activity. And to minimize your risk of pregnancy and STDs, continue to use condoms, even if you've been going out a while. I use condoms and the Pill, and it's great tp have that sort of peace of mind.