How long after you get a student loan can you refinance it?

Question
i got a student loan about a month ago...i am making payments on just the interest right now but the rate fluctuates so much that the payments are different each time. When can I refinance and lock in a fixed or lower interest rate?
Answer
Check with the company called Collegiate Funding Services. I consolidated all my student loans with them and I have a set monthly payment that I pay them until my loan is paid in full.