Hi! Many thanks for your question on eHealth forum!
The two most common cause of inter menstrual spotting are pregnancy and birth control pills. Other causes are hypothyroidism, cervical dysplasia, cervical polyps, cervicitis (infection/inflammation of cervix), vaginitis (infection/inflammation of vagina), cervical and uterine cancer, uterine fibroids, hormonal imbalance as in polycystic disease of the ovary, use of blood thinners, genital ulcers, STDs and stress.
Hence wait for your next due date and take a pregnancy test if you miss your periods. If you have normal periods, then consult a gynecologist to rule out other causes.
Hope this helps. Take care!