one month old constipated

Hi

Well my little girl has been grunting and fighting withe her little arms and legs and I could not understand why until I opened her nappy this morning while she was taking a poo and there was this round hard thing with normal poo afterwards and all the time I thought she was just a busy little girl moving around so much.

Is there anything I can give her , I know when i had my baby shower they said I must give my baby prune flavored purity but she is not near eating , only another 5 months.

If you have experienced this please let me know what I can do?

Some info , she was on breastmilk but now it has dried up and I give her formula : ISOMIL 1 if this helps in anyway.

Thanx