Thanks for consulting us.
There are a number of causes of inter-menstrual bleeding
Sex can only cause bleeding if you have a lesion inside or you acquired a tear. Infection may make your tissues friable & prone to bleeding, but, vaginal discharge
is a more likely sign.
Best way to sort this out is to see a Gynecologist & get yourself examined. Have a Pap test if not done recently.
Wish you good health.