You can buy a house, however, depending on what you mean by [poor] credit it may not be right now. You DO have options right now though. First things first, you should contact a great lender and one that works with CCCS [Consumer Credit Counseling Services). CCCS has a list of great lenders that can help you. CCCS will help you to balance your current budget, make payments on debt,make saving for a home esier and help you to control any outstanding bills.
CCCS will help evaluate your credit and tell you what you need to do, to get your credit together. They then will work directly with the lender to help you with a down payment and closing costs assistance program. This is a program designed to help you get into a house. It's a great program for people on a fixed incomes.
You DESERVE the American dream of home ownership and you can there. I would definitely recommend you speak to someone at CCCS first, there is NO CHARGE and they will help you with the first step, just tell them your goals and make it happen!
I'm glad to see you want to buy a house, many people on fixed incomes have done it, but it will take a bit of work.
Good luck and have a wonderful day!