Pelvic Pain after Sex

Elizabeth
Anyone experience this before? My husband and I were out of the house all morning shopping and went home and had sex. I took a nap afterwards and woke up with terrible pelvic pressure. Felt like really strong menstrual cramps. I am a FTM so I'm not sure what contractions feel like yet. Anyone else experience the extreme pressure after sex? I'm 35 weeks tomorrow. Should I prepare for labor soon? TIA