Why do I get lower belly pain after sex?

An achy lower belly after sex is common and usually benign: the uterus contracts with orgasm, deep penetration can bump the cervix, and pelvic muscles do real work - a mild ache that fades within hours is physiology. Recurring or significant pain after sex is a different question, and the causes overlap with painful sex generally: pelvic infections - including STIs like chlamydia, which can smolder with few symptoms before causing pelvic inflammatory disease - ovarian cysts, which ache when disturbed, endometriosis, and pelvic floor muscle spasm. The pattern-reading: a brief mild ache after enthusiastic sex, gone by morning, recurring rarely - benign. Pain that happens most times you have sex, pain that lingers into the next day, deep pain in specific positions, or pain that is new for you - worth a provider visit for an exam and STI screening, since chlamydia in particular is common, often silent, and silently harmful to fertility if untreated. Urgent patterns: severe sudden lower belly pain - especially one-sided, where ovarian torsion or a ruptured cyst sit - pain with fever or abnormal discharge, pain with abnormal bleeding, or pain with dizziness and shoulder-tip pain, which is the internal-bleeding pattern and an emergency. The NHS pelvic pain guidance draws the same line: severe or persistent pelvic pain gets assessed. Pymander is a free AI doctor, 24/7 by text. Describe the pain, when it happens, and how long it lasts, and it can help you judge the pattern.