Spotting or bleeding after sex can happen due to multiple reasons. It can be due to skin irritation, over-stretching of the vagina, STD, vagina dryness and the worst of all cervical cancer. Pain during intercourse is also associated with the growth of cancerous cells in the cervix. If you experience pain, discomfort and bleeding occasionally then there is no need to worry. However, if it is a regular thing consult your doctor.