Bleeding after sex.. Now what?

So il give a little back story, in a 18 weeks pregnant and the other day when me and SO were having sex, I began to bleed!! So of course panicked and ran to the hospital, they scanned me and everything was perfect with out little baba. Also had an internal done which showed nothing, so absolutely no explanation for why it happened. But my questions are.. Did anyone ever have this in pregnancy? And if so did ye have sex again because no doctor has told me not to but we haven't since because I'm terrified it will happen again.