Constipated

JC
My baby is a month old and constipated. I originally breastfed but about a week ago I started giving her formula. I still breastfed but I wasn't making enough milk and she was still hungry so I had to supplement. I gave her 1 once apple juice mixed with 1 once water. Than an hour later gave her half a teaspoon of karo Syrup. She pooped the next day in the afternoon. That was the last time, she is still straining and whining. So I called pedi they said to give her a suppository, so I did. She has diahreia instantly. But now she's back to straining herself. Do y'all have any remedies that work to make it go away or any techniques? I don't want to keep giving her stuff since she's still little.