Welcome to Just Answer. I am here to help you resolve your tax and finance concerns. Please feel free to ask anytime you need extra help.
You have two options here.
The first and perhaps less likely to be approved is an offer in compromise. If accepted this could reduce the amount you owe to a fraction of the present balance and be paid over a period of time. I say less likely to be approved because it would show that you have defaulted on a payment agreement three times in the past.To do this you should consult with a tax professional to discuss the possibilities.
The second choice is to renegotiate the payment agreement explaining what has happened and the need to reduce the monthly payments. At this point I would suggest the assistance of a tax professional also. The IRS will deal with a tax professional differently than they do with an individual citizen and you will likely get much better results.
The last thing to do at this point is to do nothing or try to deal with this problem all alone. The IRS will have issues with you and even your home could be at risk. Please seek professional help quickly. You can find a CPA, Enrolled Agent or Tax Attorney in your local yellow pages, on line or through the referral from a friend.