What Causes Knee Pain During Periods?

Hi, I'm 21 years old and for the past 4 years, I have experienced knee pains when I am menstruating (have my period). It is most painful the first few days, and then it stops and doesn't come back until the next month when I get my period again. I mostly feel the pain from the middle, (especially) to the bottom of the knees (the bone at the bottom).The pain at times is bearable, but there are occasions when it is strong, and I drink a strong coffee or something hot to minimize the pain, and it goes away. I barely touch paracetamols when this pain comes.
Is this normal? And if it is, how can I prevent getting them every month when I menstruate?