what's an iud

Scarlett
I have a rare blood clotting disorder which makes my periods extremely painful if you go on my page and look there is a more detailed post of what the disorder is but this disorder. Doesn't allow me to take birth control pills because it increases clotting so my doctor suggested an iud I 
Dont know much about them so if anyone could give me information or if you have one tell me what it's like or if you've had problems with it I'd love to know thanks