Mama, please see your OB soon to check what's happening, irregular periods after CS, lalo na kung may possibility ng pregnancy, kailangan talaga ng proper check-up at maybe ultrasound para ma-confirm. Negative PT doesn't always mean you're not pregnant (especially kung nag-test ka too early), pero it could also be na ang body mo pa lang ay nag-aajust after surgery, both possibilities need a doctor to sort out, hindi lang PT. Get it checked, okay?