Helpless, I am sorry you feel that way. I talk with people everyday on how to build, reestablish and improve their credit. It really isnt all that hard to do. It just takes some patience. But in time, you will be in the 700's.
First of all, have you looked at your credit report to see if there are any derogitory accounts against you? If so, that may be why you are not having any luck. You can review your credit report FREE at www.annualcreditreport.com to check for yourself without having an inquiry showing against your credit.
Another thing could be is if you recently changed your employment. Creditors like to see stability, otherwise, if you change jobs frequently, you may be looked at as high risk.
One thing you could consider is to get your alternate tradelines of credit added to your credit. This would be your light bill, phone bill, water bill, trash bill, car insurace... anything you pay on a regular basis that you know has always been paid on time for at least the last 12 to 24 months. Have those companies write a letter on your behalf on there letter head stating how long you have had the account and what your average monthly payment is. Make sure it shows 0x30 for any late payments. In doing so, the creditors who are looking at your credit the, will see your ability to pay the other bills on time.
If you want, you can email me directly at yourhomemtg@aol.com and I will send you back a copy of my FREE Credit Readiness Program without any further obligation. I give them out all the time, including at the free credit seminars I do. It will help you to understand your credit better and how to make the most of it. I have closed many loans with people who I gave it to and let them strengthen their credit with so they could qualify to buy a home.
Good luck!