Irregular period

I am currently 8 days late on my period and 4 months post partum. I am aware that periods are irregular after childbirth. But last month it was closer to the time this app told me that I would get it. And now its later than last month. I'm getting somewhat concerned as I had my tubes clamped the day after I gave birth to my daughter. I know nothing about periods after birth as I got an iud after my son. So I'm just trying to see if this is normal and I'm just freaking out for no reason, or if I should go get checked out because it's not normal and I could possibly be pregnant, and since my tubes were clamped it would be ectopic.