Are Acute Cramps During Exercise Normal After Implantation Of IUD?

I had a copper coil fitted almost a month ago and it has been OK except for occasional cramps. Today though I went to the gym and I was unable to do my usual routine because of the pain in my uterus. I tried to do it very gently and still I had to go back home by taxi after 20 minutes because of the pain. I haven't been going to the gym so regularly since I got the coil, so I am not sure if the cramps have to do with the exercise or with the fact that my period is due in 3 days. In general I am not sure if it is normal to have such acute cramps that you have to sit down. Thank you for your help.