How how is the judge able to determine and modify my income?

I live in Colorado and I have the child 280 days out of the year. The father requested a motion to modify child support in hopes of having it reduced. He is remarried with three more children. The initial court hearing child support went up by $200 a month. The father contested and stated he was treated unfairly because he is self-employed. I was working a W-2 job at the initial request of documents and submitted those. In court the father stated that it was unfair for me to not turn over my IRS returns. Please note the father is self-employed therefore he had to turn in tax forms. The judge continued the first court hearing to allow the father to have access to my tax returns. Last court hearing in January my employment had changed and I am working part time making $20 an hour. I am also starting a new business with money that was invested by other people. During the court hearing the judge determined I was capable of working full time making $20 an hour. By the end of the judge determined I made $4,000 per month. Absolutely unreal amount in my area.