Welcome to HealthcareMagic
Sometimes in mid cycle there may be some spotting due to ovulation and its normal thing. Ovulation bleeding usually lasts for only 2-3 hours and may be so slight as to cause only a brownish discharge that stains the underclothes. As u have not mentioned duration of your cycle its difficult to comment. If you have doubts you can take emergency contraceptive pill
because last intercourse was unprotected and roughly at the time of ovulation. Emergency contraceptive pill should be taken within 72 hrs of last intercourse. Take care.