Constipated 3 month old

So my 3 month old boy was having some inconsolable crying fits and was also refusing to eat right after them. I called his pediatrician and they said to put him on soy formula. He has been switch to 3 different formulas since he was born and the one before soy he was doing great! It was the nutramigen broken down formula.

I didn't believe it was the formula, but I didn't argue further and I switched to soy. It's been 3 days. The last 2 days my son has been trying so hard to poop and screaming and crying when he tries . Even when he gets some out, he's screaming the whole time and it's hard and clay like and very very little amount

What can I do until tomorrow when his doctor opens? I don't want to take him to the ER and risk his health more.