Noticed A Cracking Sound From The Knee & Also Pain When Pressure Is Applied

I am a 24 year old female and do horseback riding. I ve been having some issues with cracking sounds coming from my knees - and sometimes pain when it occurs - whenever I climb up stairs. I m also unable to keep my knees bent only slightly (standing upright but knees bent) for a long period of time, before pain sets in. I ve been riding since 2007 and have never had this problem before, it only became apparent recently. Could it be because of an iron deficiency? I had to take iron supplements a few years ago for a period of 3 months and picked up some more this morning because a few of the other symptoms I m experiencing also seem to point to iron deficiency. Kind regards