Periods after a pregnancy are very abnormal until a year later. Your period will be late a lot, but it's just your body trying to go back to normal. My period was 3 weeks late but still came.

your periods may just not be on track yet I had my twins 3 months ago and my last period I was 2 weeks late

blood work although that STILL doesn't always say... I was 12 weeks before any test showed positive

so

take another one in a week or sk

Go get blood work done