What Causes Severe Period Like Cramps After Having Sex?

I have two daughters (healthy pregnancies, healthy births). 6 weeks after my second was born I tried to have a coil fitted, but the doctor couldn t insert it, saying my cervix was too tightly closed. She said she had never seen this in someone who had recently had a baby. I ve now been trying for number 3 for 6 months. I keep getting cramps like period pains, all through the month, mostly the day after having sex. Is this all linked?