200 point drop in two months

Good evening,

Thank you for answering my question. What can I do? I had a credit score of 670 two months ago. My mortgage lender said I need a 700. He suggested a credit card. I got two. I used one sparingly. My credit score is now down to 540! My other categories on my statement are all excellent: history, usage, marks, etc. What can I do to get my first house?