What Are The Chances Of Getting Pregnant With IUD?

Hi my name is Anjelika my last period was April 7. I am having bad abdominal cramps, lower backache, nausea, and i am currently on the IUD. I have looked for my IUD strings and i wasn't able to find them at all. I've been having pain while having sex with my partner. Can i be pregnant again? When should i expect my next period?