Brief Answer:
It is reaction of uterus to the biological molecules in the semen.

Detailed Answer:
Hello Ms XXXXXXX

Welcome to Ask A Doctor service and thank you for posting your health query.

I have read through your concern carefully and understand your issue very well.

Semen consists of sperms and other biochemical molecules which initiate a series of events in the vagina and uterus that results in elimination of most of the sperms allowing only a few sperms to travel upwards through the uterus to reach the Fallopian tubes where they come into the vicinity of the ovum (egg) and fertilise that ovum.

Part of that response includes the rhythmic contraction of the uterus to propel some of the sperms upwards and rest are expelled.

Since the IUD was placed while you were virgin, this rhythmic contraction becomes pronounced due to the presence of the IUD, the uterus tries to expel the IUD so it contracts forcefully resulting in cramps.

Allow for your uterus to get used to the presence of the IUD (it may take an year), however, please note that these cramps may persist till the time IUD is in place.

You can take the same medicines that give you relief.

Do check for the thread once in a while to make sure you can feel it, that will assure you that the IUD is within the uterus.

If the pain gets worse, or if you notice bright red bleeding following intercourse or these cramps, please do go to the emergency to rule out perforation.

I hope this answers your concern. Do revert if you have any more doubts.

Wishing you good health and happy life ahead.

Best regards

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