It didn't take long at all for my libido to return- maybe a week or two. The insertion process itself was fairly painful (I'd suggest having someone drive you home) and my body felt out of sorts for a good 24 hours. I experienced some bleeding, but not much, and again, only for a day or so. I've had this IUD for almost 4 years and haven't had any problems. I also used to get a lot of migraines when I was on the pill, more than once a month- now I get only one or two a year.
Depending on what your schedule is like you could probably have Mirena inserted in the evening after your run(s), take the next day off, and be back to running the day after that. I did that and it worked out just fine!