After income of second job

I have been divorced 5 years with 3 small children. While we were married I worked a second job to help put her through school. She acquired her bachelors’ degree and got a good job. Per our arrangement once she graduated I started going to school part time. It was not long after this that she wanted a divorce. We split up, I paid my child support on time every month and slowly put myself through school and finally got my associates degree last year. 3 years ago she filed a child support modification order. The amount of child support I paid substantially increased.
I have been living in a small 1 bedroom apartment and up until this time I had been I had gone through 2 old cars that continually broke down. I had finally come upon the decision that I needed to buy a newer car that was more reliable and bought a year old Corolla. This required me to get a second full time job in order to pay for this.
After a few months of working an average of 18 hours per day to make ends meet. I recently received a notice again of Modification of Child Support. Her attorneys are trying to tell me that my income is higher now because of my second job and that amount is included in the new amount I now have to pay her. Hiring an attorney is out of the question as I very simply don’t have any money. It doesn’t take a rocket scientist to figure out that if I have pay the amount they are asking for, the numbers will not add up and I will either lose my car and of course lose my job shortly thereafter or I will have to move out of my apartment and have no where to go.
How can they do this? I am simply trying to make ends meet. My ex and her husband don't need the money.
HELP!!!

You could go into court yourself and show your budget, how many hours you are working etc. The judge will likely not make a change if you working that hard just to get caught up basically. But have all your expenses and income mapped out.

thanks for the advice. The hearing is at the end of the week and I have been putting together all the financial stuff. wish me luck!

Let us know what happens!

There is something really wrong with the legal syste. I went into court last Friday afternoon. My ex-wife and her husband talked at length about the rising expenses of raising children. The rising costs of daycare and on an on. I presented my list of living expenses, receipts, my bank book, paystubs, etc... This included a break down of everything and how it shows I am barely scraping by. The judge (female-although it shouldn't matter) favored my ex and made the decision of $150.00 a month more. They also tried to disqualify the money spent on medical insurance that I pay every week. I am on a family plan due to the number of dependents (my kids). Even without me on it, the amount would have been the same. They did deduct $20.00 off of it. I know for a fact my ex makes almost 3 times the amount that I do, her husband also does quite well. This has left me in the spot where I have my rent covered through August. After that, I don't know. I have been trying to make some sense of this. The courts do favor the mother. At 34 years old I may probably end up living with my elderly parents.
signed: screwed again in Texas.

I had a question for anyone to answer (if they know it); Why (according to the court) is it none of my business what income level my ex and her husband are at?

It is based on her income and/or abililty to earn, not that of any new spouse.