3 months postpartum

Angela

My son was born April 23. In June I got my first period. July’s hasn’t come. According to <a href="https://play.google.com/store/apps/details?id=com.glow.android">glow app</a> I am late by a week. I’m not pregnant I took 2 tests and both negative. I have strong cramps and back pain. Could it be come late? Is my body still regulating from having my son? Please help me.