ps....I am now 21 weeks preg.
If your coming off Mirena the manufacturers say you can fall pregnant straight away, however, from personal experience I would wait for 3 cycles. I fell within 2 weeks of removal, but I miscarried that one, so all up it took me 6 months to fall pregnant after removal. All women are different But the good news is, you can have sex straight away! Good luck.
As far as i know you can have sex right away, although when I went off of birth control my Dr. recommended waiting 3 months to start trying to conceive. That was several years ago though, and I was on a different form, so i would check with him or her. As for how long to get pregnant? Everyone seems to be different when they come off of birth control. Many women do find they have irregular cycles for a while as their body regulates itself again, and that can make it a bit challenging.