Brief Answer:
It could be due to hormonal imbalance.

Detailed Answer:
Hello dear,
Thanks for trusting us about your wife health care.
I have gone through your history and understand your concerns.
Irregular menstrual cycle after delivery of baby could be due to hormonal imbalance.
It could be due to Anaemia also, get her blood test like haemogram and thyroid profile and review with report.
Get your pelvic ultrasound to rule out the cause of the same.
Eat lots of vegetables and fruits and drink a lot of warm water.
Hope found useful, feel free to ask more information.
Good luck
Regards

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