If you are not already taking Glucosmine Sulfate, I would highly recommend it. It should be okay with breastfeeding but you could double check with your doctor or put in a search online. I had terrible knee problems for years and even quit running. My knees worsened and I even had to use a cane during my 5th pregnancy. After my last child was born, I went to an orthopedist and then to physical therapy to strenghen the muscles that support the knees. A year later, I ran my first marathon but still had knee problems. My cousin, an RN gave me a bottle of glucosomine. It has been like a miracle for me! I've been using it for about 7 years. I seldom have any knee problems now. You may also find that just putting some doctor Scholl's inserts in your shoes will help too.
If you don't mind going to Glendale to see a chiropractor, I'd be happy to give you my chiropractor's number. Her pricse are very reasonable, she's down to earth, and she truly cares about her patients. She may be able to do some ultrasound on your knee. Email me if you want her information.