I have found that CONSUMER ACTION is an excellent resource for objective advice on all things credit related. You'll find free and sincere advice on everything from settling collection accounts to rebuilding credit to building credit from scratch on their website. http://consumer-action.org/
Beware of anyone offering to "repair" your credit! The Federal Trade Commission issued a stern warning last year that such offers are scams. Find more from the FTC HERE. http://www.ftc.gov/bcp/edu/pubs/consumer/credit/cre13.shtm
The best way to buy a home is to have a decent credit history combined with sufficient Income and Assets for a home purchase.
The best way to have a decent credit history is to settle negative outstanding obligations and pay all your bills on time for at least two years.
It sounds certainly like you are determined, hang in there!
You say in your question that their are no negative accounts on your credit report. A bankruptcy is a negative trade line as well as all the accounts that were included in the bankruptcy. These are all negative trade lines and causing a drag on your credit rating. Both your score and your credit rating are in dire need of credit repair and credit education.
I invite you to look over some blogs I have written on Trulia for credit repair and credit score boosts. You would benefit from both.
I would suggest you begin with credit restoration services to see if some of the negative trade lines listed on your credit report can be removed as well as the bankruptcy itself. Also a 620 credit score will qualify you for an FHA mortgage however you are going to pay a lot higher interest rate because the score is still considered poor.
A better credit score of 680 will lower the interest rate substantially on the mortgage loan. The interest rates will even get more attractive at 720 credit score and 749 credit score. Of course it's up to you and many mortgage brokers out there will be happy to place you in a high interest loan with a poor credit rating of 620.
I certainly wish you good luck however, I would again invite you to look into credit education and credit repair for your financial future. It's your money.
The Credit Restoration Expert