IB question

I just had our son 2 1/2 months ago. I got my first period 7 weeks pp. Lasted 3 days. Last week i had brown spotting for 3 days, i figured my af was coming. It hasnt. Could it possibly be IB? We arent trying but arent preventing either. But af should be here now id assume. I wanna wait til the 1st to test. But not sure if thats gunna be to long to wait. So i guess my question is how long after IB do you ladies typically test?