Hardness Abdomen area that comes and goes - Breastfeeding mom

[geetabora]

I have been breastfeeding from last 3 months but today noticed some hardness in stomach area / abdomen that lasts for couple of hours and then goes of. Its strange that a part of her abdomen gets hard for some time and then it clears of.

After some time another part of abdomen gets hard and then it goes off. Not able to understand this, anyone here who had the same problem before ?

Thanks