First food constipation

So my son’s pediatrician gave me the green light to start purées once he is 20 weeks old.

It has been a week, was trying different vegetable every few days so far we tried zucchini, carrots peas

And tonight it’s my baby’s third night without pooping

I’m a FTM and I’m panicking and regretting starting solids before he passes 6 months!

Is it normal to have constipation with solids and what are the solutions for it?