If you google this, you'll find a lot of women in your situation, and few seem to ever get answers.
Gushing fluid isn't a symptom of early pregnancy, so you can probably let that fear rest.
Accumulation of fluid in the uterus can be related to Pelvic Inflammatory Disease, fibroid tumors or cervical erosion (you're too young for that).
The timing of this happening several days after unprotected sex does indicate an infection, in my opinion. Do you have a doctor you can go to?