I Don’t Know How I’m Not Pregnant

When me and my boyfriend have sex we make it last at least an hour! We make sure we have multiple orgasms each, last night he fucked me for an hours and a half and he came in me 4 times and let me tell you, I was filled and dripping when he was done with me. I have a IUD in but there’s like a million sperm per cum load and he did 4 in me so there’s obviously a few million swimmers inside me and how do they all get killed by the IUD? It just amazes me!!