Hey, It's Been 3 Weeks Since I've Had Sex. We

Hey, it's been 3 weeks since I've had sex. We didn't use protection and I'm not on the pill. My period came a week after, as planned, but was only 3 days long instead of 5, and now i feel nauseous and I'm bleeding, it's gooey but the same color as a regular period. What's going on?