back when I was 34, both of my knees swelled up and I could not even get out of a chair. I had a 4.5 lb preemie to take care of and an upstairs to deal with. Our home is on a hill besides, and we have to climb those stairs to even get in.

I had a C-section to recover from too. The only explanation at the time for me was that I had RA before and this was a flare following pregnancy. Or that the hydralazine I had to take for blood pressure caused a pseudo Lupus. But my blood work had been done before my pregnancy because I was already having arthritis issues, just nothing really swollen red and hot (inflamed) and the tests were negative. In those days, Motrin was very new, just came out. So that is what I was given. Along with a boatload of other blood pressure drugs. It took over 6mos for my knees to get better, but they have never been the same. I had to put in a small nursery on the main floor, and I was mostly housebound for the first 3 months. But luckily for me, the inflammatory attack did subside, and I have negative RA factor and no ANA elevations.

My bowling and tennis days ended then. But eventually I did return to work when my son was 5 yrs. old. I have had knee issues ever since, but I have learned to live with them. So far I have avoided a replacement.

My son was born blind, so we had to deal with that too. So I just focused on him, and did the best I could. My husband has been very helpful, and he did most of the grocery shopping in those days. He even drove us to the doctor (my son had many visits early on being a preemie) for a while.

This season my husband found me a ramp...to help me in and out of our pontoon boat, since I cannot step up higher than about 12inches and sometimes I need to where we are upNorth. Last year our water levels dropped suddenly in August and the dock was too high for me to get up to.
I have been lucky in not needing my cane lately, but sometimes I do have bad times and need it. I just am grateful for when I don't.

Some medical things that happen to people are mysteries.
Sometimes there are no answers, only labels.
In your case you have a negative biopsy so far, which is a good sign. (not a guarantee--but still good).
Many times things are self limiting. Your body can heal itself, and it does. This may happen for you or not. Only time will tell.

adding... I would think you would have had the autoimmune testing done by now...typically rheumatologists do this. But some have false positives, and false negatives...The RA factor is one of those with a 70% accuracy rate. While you wait for the neuro... why not see if you can get a rheumatology consult?