Oh poor you. This happened to me - I had a mirena coil, it fell out, I got pregnant with no3.
It was a ghastly pregnancy (that's why I had a coil, I don't "do" pregnant well! I spent half the pregnancy and a good chunk of the following year in hospital (I had a pregnancy related kidney problem. Oh, and pnd,which isn't surprising in the circumstances!). Things were so bad, dh had a vasectomy which they agreed to even before she was born!
Now I'm looking at it from behind, and yes it was hard. But I have my gorgeous, pretty, enthusiastic, fantastic dd2, who is 9. It was a very, very hard couple of years - I wish I could have skipped it - but every horrible second was worth it because of her! And she's had her own (totally unrelated) problems, a hip condition, but we all muddle through.
She has a fabulous bigger sister (13) and brother (11) so yes, I had a newborn dd2, 22 month old ds and dd1, 9 weeks off tiring 4!. It was, as I said, hard work. But totally, totally worth it!!