irregular, labor like pains, very severe, no diagnosis!

I have very sharp pain (like someomething pulling and wants to come out) between my lower abdomen and my anus. It is so severe that I will not be able to move. Then it goes away and might not happen in months. This started a few years ago after my third child and the first time I used a coil. It is so irregular that my doctor says they don't know what is wrong. It is similar to labour pains. It lasts for about 5 minutes. Since i remove dthe cild almost 2 yearsago it has not happened and now 4 months after my 4th child I suddenly have the pain again. The only other time I had the pain recently was just before I got pregnant and my gynae did a procedure to check if I have eggs and this was the most severe time as I could not walk for about 10 minutes. This happened about 30 minutes after the procedure when I got home.