Breastfeeding and Plan b?

I've been breastfeeding my son for 15 months now, and a few days before he turned 14 months I started my first period since having him, but it was more of a spotting for 3 days, then stopped for 4 days and then more spotting for 4 days. I'm pretty sure I'm ovulating right now because all of a sudden my sex drive came back and it's been nonexistent since I've given birth and I have clear discharge. Anyways long story short I finished my birth control pills almost 3  weeks ago and since we just moved ( my husband is military) I haven't been able to schedule an appointment to refill yet and we had sex twice today using the pullout method. The second time, although he pulled out he was a little worried that some might of come out inside of me and since another baby is the last thing we want right now he asked about the plan b pill...but I have no idea if it's safe to take while breastfeeding. Keep in mind my son nurses a lot still and I feed on demand so I have no stored milk for him. Any help is appreciated, TIA!