My sister went into labor after having sex.

Sex doesn't induce labor... the activity/orgasm can induce cramping. The sperm can thin out the cervix.

Your pressure & cramping is completely normal after sex. But of course, if you're concerned call your doc and/or get checked out. Better safe than sorry.

I felt that everytime I had sex close to my due date. Sometimes it was so bad I could barely walk from all the cramping and pressure. It usually went away after a few hours or by the next day. I would monitor it and see how you feel in a little bit.

You need to call your doctor.