How do I modify a child support order

I have been divorced from my ex-husband for 4 1/2 years. I have not worked in almost two years. I was laid off and then, I have had two surgeries and am unable to work. My ex was given a promotion and placed on salary. At the same company. In our divorce agreement, I am to pay for half of the children's health insurance and half of the cost of their healthcare. I do not work. The only income I have is from my child support. $145 per week for two children. My ex has not given me any proof as to what he pays for insurance and he has refused. He takes $45 every week from my check and will not cooperate with the requests (via certified mail) for proof of the amount of insurance being deducted from his check each week.

I do not have the funds to continue paying for the insurance and he refuses to even discuss letting the insurance be his sole responsibility. I want to know if there is a way to collect on the money that he continually without my approval deducts from my check each week and if there is a way to increase the amount of child support each week. I need help bad. Does the fact that his new wife makes more money and he makes more than he did justify filing for more support. I am married and my husband works. Would that hurt my case for more support?