Hello,
Having normal knee xray and normal blood results tells us that you don’t have a fracture or bony infection/inflammatory condition respectively.
However, we can’t see the internal ligaments on X-ray and any derangement in the ligaments could be a cause of your pain. Again ligament damage in both knees is uncommon without any trauma like in your case.
Next Steps
A clinical examination to see the exact cause of your pain is needed.