Is this normal?

I’m 36w3d (or 37w1d, switched OBs and they used different EDD) and I started bleeding while having sex. I’ve had extremely light, pink spotting after sex once or twice but this was full on bleeding within a few minutes of starting. Luckily it didn’t last.

I ended up cramping and having contractions for about an hour and a half afterwards then fell asleep, but I woke up with pretty heavy cramping during the night.

Is this normal, or should I be worried?