What could cause a teeny blood clot to pass two days in a row, while not on period? not on bc and not sexually active. also, no pain. thanks!

Likely no problem: Having 2 episodes of scant spotting usually doesn't mean a problem. The likeliest cause is your hormones were off a little so didn't hormonally support the lining of the uterus as well so spotting occurred. This is a normal variation. Another cause can be a benign growth in the lining if the uterus called a polyp. This is best found by an ultrasound. If spotting doesn't resolve see a doc for exam.