What can cause a low grade fever every 7 to 10 days?

Need more info. What's low grade? Recurring fever is usually a sign of a significant problem, especially if you have other symptoms or problems. Some infections such as malaria can do this, relapsing mediterranean fever (rare). Some inflammatory condition even like rheumatoid arthritis can do it. Some cancers like lymphoma come to mind. If you feel fine, some people just have higher 'normal" temperatures.