I used normal dishwasher liquid for all my 4 kids and yes, they're fine too! Just make sure to thoroughly wash the bottle. It could be the milk that causes the constipation. Gently massage your baby's tummy downwards @ the same time when she is trying to poop to ease the struggle. Use minyak telon front and back also after bathing. I normally will massage some on the butt too cos minyak telon is heaty and it really helps.
We just use normal liquid since birth.. all my 3 kids are fine