period & breastfeeding?

Advice? I've had my period back for about 4 months now and it's always been super reg. My daughter will be 9 months tom and we nurse about 5-6 times daily and quite a bit through the night. this month it's 3-4 days late so far. What's going on? No I haven't tested bc we have only had sex twice? I think and we use pullout method. (I know it only takes one time and I know that's not the greatest form of bc but we have used it for 4 years on and off and it has never failed us) as long as you use it correctly there's a pretty good chance of it working. I just don't know if it's my body or if it's worth just going out for a test just yet. Thanks for any replys