My partner and i had sex about 4 hours ago and about 30 minutes after we finished I began having really bad lower back pain, it still hasn’t gone away.

I know cramping after sex can be normal, but should I still be cramping 4 hours later? Or could this back pain be the result of something else like early contractions/the start of back labour?

I haven’t had any abdominal cramping or other signs of labour.