Your symptoms could be due to the excess progesterone
that is present in this part of the cycle. They are suggestive of premenstrual symptoms. Your swollen knee
could be an inflammation and you should get it treated with an orthopedic. Since you are unprotected pregnancy
cannot be ruled out, so you can go for a HPT, but you can wait till your period is due since your cycles are regular. Please consult your doctor for further advice. Good luck.